Reformat comments of non-public serde_derive internals

Fixes these being treated as "tests" by `cargo test` in serde_derive:

    running 3 tests
    test src/internals/check.rs - internals::check::check_remote_generic (line 23) ... FAILED
    test src/internals/check.rs - internals::check::check_remote_generic (line 29) ... FAILED
    test src/lib.rs - (line 3) ... ok

    failures:

    ---- src/internals/check.rs - internals::check::check_remote_generic (line 23) stdout ----
    error: unknown start of token: \u{2026}
     --> src/internals/check.rs:25:20
      |
    4 | struct Generic<T> {…}
      |                    ^

    error: cannot find attribute `serde` in this scope
     --> src/internals/check.rs:24:3
      |
    3 | #[serde(remote = "Generic")]
      |   ^^^^^
      |
      = note: `serde` is in scope, but it is a crate, not an attribute

    error[E0392]: parameter `T` is never used
     --> src/internals/check.rs:25:16
      |
    4 | struct Generic<T> {…}
      |                ^ unused parameter
      |
      = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
      = help: if you intended `T` to be a const parameter, use `const T: usize` instead

    ---- src/internals/check.rs - internals::check::check_remote_generic (line 29) stdout ----
    error: unknown start of token: \u{2026}
     --> src/internals/check.rs:31:21
      |
    4 | struct ConcreteDef {…}
      |                     ^

    error: cannot find attribute `serde` in this scope
     --> src/internals/check.rs:30:3
      |
    3 | #[serde(remote = "Generic<T>")]
      |   ^^^^^
      |
      = note: `serde` is in scope, but it is a crate, not an attribute

serde_derive/src/internals/check.rs

@@ -3,8 +3,8 @@ use internals::attr::{Identifier, TagType};
 use internals::{ungroup, Ctxt, Derive};
 use syn::{Member, Type};
 
-/// Cross-cutting checks that require looking at more than a single attrs
-/// object. Simpler checks should happen when parsing and building the attrs.
+// Cross-cutting checks that require looking at more than a single attrs object.
+// Simpler checks should happen when parsing and building the attrs.
 pub fn check(cx: &Ctxt, cont: &mut Container, derive: Derive) {
     check_remote_generic(cx, cont);
     check_getter(cx, cont);
@@ -17,18 +17,18 @@ pub fn check(cx: &Ctxt, cont: &mut Container, derive: Derive) {
     check_from_and_try_from(cx, cont);
 }
 
-/// Remote derive definition type must have either all of the generics of the
-/// remote type:
-///
-///     #[serde(remote = "Generic")]
-///     struct Generic<T> {…}
-///
-/// or none of them, i.e. defining impls for one concrete instantiation of the
-/// remote type only:
-///
-///     #[serde(remote = "Generic<T>")]
-///     struct ConcreteDef {…}
-///
+// Remote derive definition type must have either all of the generics of the
+// remote type:
+//
+//     #[serde(remote = "Generic")]
+//     struct Generic<T> {…}
+//
+// or none of them, i.e. defining impls for one concrete instantiation of the
+// remote type only:
+//
+//     #[serde(remote = "Generic<T>")]
+//     struct ConcreteDef {…}
+//
 fn check_remote_generic(cx: &Ctxt, cont: &Container) {
     if let Some(remote) = cont.attrs.remote() {
         let local_has_generic = !cont.generics.params.is_empty();
@@ -39,8 +39,8 @@ fn check_remote_generic(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// Getters are only allowed inside structs (not enums) with the `remote`
-/// attribute.
+// Getters are only allowed inside structs (not enums) with the `remote`
+// attribute.
 fn check_getter(cx: &Ctxt, cont: &Container) {
     match cont.data {
         Data::Enum(_) => {
@@ -62,7 +62,7 @@ fn check_getter(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// Flattening has some restrictions we can test.
+// Flattening has some restrictions we can test.
 fn check_flatten(cx: &Ctxt, cont: &Container) {
     match &cont.data {
         Data::Enum(variants) => {
@@ -101,12 +101,12 @@ fn check_flatten_field(cx: &Ctxt, style: Style, field: &Field) {
     }
 }
 
-/// The `other` attribute must be used at most once and it must be the last
-/// variant of an enum.
-///
-/// Inside a `variant_identifier` all variants must be unit variants. Inside a
-/// `field_identifier` all but possibly one variant must be unit variants. The
-/// last variant may be a newtype variant which is an implicit "other" case.
+// The `other` attribute must be used at most once and it must be the last
+// variant of an enum.
+//
+// Inside a `variant_identifier` all variants must be unit variants. Inside a
+// `field_identifier` all but possibly one variant must be unit variants. The
+// last variant may be a newtype variant which is an implicit "other" case.
 fn check_identifier(cx: &Ctxt, cont: &Container) {
     let variants = match &cont.data {
         Data::Enum(variants) => variants,
@@ -189,8 +189,8 @@ fn check_identifier(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// Skip-(de)serializing attributes are not allowed on variants marked
-/// (de)serialize_with.
+// Skip-(de)serializing attributes are not allowed on variants marked
+// (de)serialize_with.
 fn check_variant_skip_attrs(cx: &Ctxt, cont: &Container) {
     let variants = match &cont.data {
         Data::Enum(variants) => variants,
@@ -264,10 +264,9 @@ fn check_variant_skip_attrs(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// The tag of an internally-tagged struct variant must not be
-/// the same as either one of its fields, as this would result in
-/// duplicate keys in the serialized output and/or ambiguity in
-/// the to-be-deserialized input.
+// The tag of an internally-tagged struct variant must not be the same as either
+// one of its fields, as this would result in duplicate keys in the serialized
+// output and/or ambiguity in the to-be-deserialized input.
 fn check_internal_tag_field_name_conflict(cx: &Ctxt, cont: &Container) {
     let variants = match &cont.data {
         Data::Enum(variants) => variants,
@@ -313,8 +312,8 @@ fn check_internal_tag_field_name_conflict(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// In the case of adjacently-tagged enums, the type and the
-/// contents tag must differ, for the same reason.
+// In the case of adjacently-tagged enums, the type and the contents tag must
+// differ, for the same reason.
 fn check_adjacent_tag_conflict(cx: &Ctxt, cont: &Container) {
     let (type_tag, content_tag) = match cont.attrs.tag() {
         TagType::Adjacent { tag, content } => (tag, content),
@@ -332,7 +331,7 @@ fn check_adjacent_tag_conflict(cx: &Ctxt, cont: &Container) {
     }
 }
 
-/// Enums and unit structs cannot be transparent.
+// Enums and unit structs cannot be transparent.
 fn check_transparent(cx: &Ctxt, cont: &mut Container, derive: Derive) {
     if !cont.attrs.transparent() {
         return;