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/block-builder/src/lib.rs

@@ -19,6 +19,8 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
+extern crate alloc;
+
 use sp_inherents::{CheckInherentsResult, InherentData};
 use sp_runtime::{traits::Block as BlockT, ApplyExtrinsicResult};
 
@@ -44,7 +46,7 @@ sp_api::decl_runtime_apis! {
 		/// Generate inherent extrinsics. The inherent data will vary from chain to chain.
 		fn inherent_extrinsics(
 			inherent: InherentData,
-		) -> sp_std::vec::Vec<<Block as BlockT>::Extrinsic>;
+		) -> alloc::vec::Vec<<Block as BlockT>::Extrinsic>;
 
 		/// Check that the inherents are valid. The inherent data will vary from chain to chain.
 		fn check_inherents(block: Block, data: InherentData) -> CheckInherentsResult;