sp-std removal from substrate/primitives (#3274)

This PR removes sp-std crate from substrate/primitives sub-directories.

For now crates that have `pub use` of sp-std or export macros that would
necessitate users of the macros to `extern crate alloc` have been
excluded from this PR.

There should be no breaking changes in this PR.

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/primitives/consensus/aura/Cargo.toml

@@ -24,7 +24,6 @@ sp-application-crypto = { path = "../../application-crypto", default-features =
 sp-consensus-slots = { path = "../slots", default-features = false }
 sp-inherents = { path = "../../inherents", default-features = false }
 sp-runtime = { path = "../../runtime", default-features = false }
-sp-std = { path = "../../std", default-features = false }
 sp-timestamp = { path = "../../timestamp", default-features = false }
 
 [features]
@@ -38,7 +37,6 @@ std = [
 	"sp-consensus-slots/std",
 	"sp-inherents/std",
 	"sp-runtime/std",
-	"sp-std/std",
 	"sp-timestamp/std",
 ]