Add FIXME to fix dead_code warning when using serde(remote)

warning: field `0` is never read
       --> test_suite/tests/test_remote.rs:143:24
        |
    143 | struct PrimitivePubDef(u8);
        |        --------------- ^^
        |        |
        |        field in this struct
        |
        = note: `#[warn(dead_code)]` on by default
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    143 | struct PrimitivePubDef(());
        |                        ~~

    warning: field `0` is never read
       --> test_suite/tests/test_remote.rs:162:20
        |
    162 | struct TuplePubDef(u8, #[serde(with = "UnitDef")] remote::Unit);
        |        ----------- ^^
        |        |
        |        field in this struct
        |
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    162 | struct TuplePubDef((), #[serde(with = "UnitDef")] remote::Unit);
        |                    ~~

    warning: field `0` is never read
       --> test_suite/tests/test_remote.rs:200:13
        |
    200 |     Variant(u8),
        |     ------- ^^
        |     |
        |     field in this variant
        |
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    200 |     Variant(()),
        |             ~~

    error: field `0` is never read
       --> test_suite/tests/test_gen.rs:390:23
        |
    390 |     struct StrDef<'a>(&'a str);
        |            ------     ^^^^^^^
        |            |
        |            field in this struct
        |
    note: the lint level is defined here
       --> test_suite/tests/test_gen.rs:5:9
        |
    5   | #![deny(warnings)]
        |         ^^^^^^^^
        = note: `#[deny(dead_code)]` implied by `#[deny(warnings)]`
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    390 |     struct StrDef<'a>(());
        |                       ~~

test_suite/tests/test_remote.rs

@@ -140,6 +140,7 @@ struct PrimitivePrivDef(#[serde(getter = "remote::PrimitivePriv::get")] u8);
 
 #[derive(Serialize, Deserialize)]
 #[serde(remote = "remote::PrimitivePub")]
+#[allow(dead_code)] // FIXME
 struct PrimitivePubDef(u8);
 
 #[derive(Serialize, Deserialize)]
@@ -159,6 +160,7 @@ struct TuplePrivDef(
 
 #[derive(Serialize, Deserialize)]
 #[serde(remote = "remote::TuplePub")]
+#[allow(dead_code)] // FIXME
 struct TuplePubDef(u8, #[serde(with = "UnitDef")] remote::Unit);
 
 #[derive(Serialize, Deserialize)]
@@ -196,6 +198,7 @@ struct StructConcrete {
 
 #[derive(Serialize, Deserialize)]
 #[serde(remote = "remote::EnumGeneric<u8>")]
+#[allow(dead_code)] // FIXME
 enum EnumConcrete {
     Variant(u8),
 }