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/state-machine/src/backend.rs

@@ -23,13 +23,13 @@ use crate::{
 	trie_backend_essence::TrieBackendStorage, ChildStorageCollection, StorageCollection,
 	StorageKey, StorageValue, UsageInfo,
 };
+use alloc::vec::Vec;
 use codec::Encode;
 use core::marker::PhantomData;
 use hash_db::Hasher;
 use sp_core::storage::{ChildInfo, StateVersion, TrackedStorageKey};
 #[cfg(feature = "std")]
 use sp_core::traits::RuntimeCode;
-use sp_std::vec::Vec;
 use sp_trie::{MerkleValue, PrefixedMemoryDB};
 
 /// A struct containing arguments for iterating over the storage.
@@ -179,7 +179,7 @@ pub type BackendTransaction<H> = PrefixedMemoryDB<H>;
 /// to it.
 ///
 /// The clone operation (if implemented) should be cheap.
-pub trait Backend<H: Hasher>: sp_std::fmt::Debug {
+pub trait Backend<H: Hasher>: core::fmt::Debug {
 	/// An error type when fetching data is not possible.
 	type Error: super::Error;