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/mixnet/src/lib.rs

@@ -20,5 +20,7 @@
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 
+extern crate alloc;
+
 pub mod runtime_api;
 pub mod types;

substrate/primitives/mixnet/src/runtime_api.rs

@@ -18,7 +18,7 @@
 //! Runtime API for querying mixnet configuration and registering mixnodes.
 
 use super::types::{Mixnode, MixnodesErr, SessionIndex, SessionStatus};
-use sp_std::vec::Vec;
+use alloc::vec::Vec;
 
 sp_api::decl_runtime_apis! {
 	/// API to query the mixnet session status and mixnode sets, and to register mixnodes.

substrate/primitives/mixnet/src/types.rs

@@ -17,9 +17,9 @@
 
 //! Mixnet types used by both host and runtime.
 
+use alloc::vec::Vec;
 use codec::{Decode, Encode};
 use scale_info::TypeInfo;
-use sp_std::vec::Vec;
 
 mod app {
 	use sp_application_crypto::{app_crypto, key_types::MIXNET, sr25519};
@@ -90,8 +90,8 @@ pub enum MixnodesErr {
 	},
 }
 
-impl sp_std::fmt::Display for MixnodesErr {
-	fn fmt(&self, fmt: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
+impl core::fmt::Display for MixnodesErr {
+	fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
 		match self {
 			MixnodesErr::InsufficientRegistrations { num, min } =>
 				write!(fmt, "{num} mixnode(s) registered; {min} is the minimum"),