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/test-primitives/Cargo.toml

@@ -21,7 +21,6 @@ serde = { features = ["derive"], optional = true, workspace = true }
 sp-application-crypto = { path = "../application-crypto", default-features = false }
 sp-core = { path = "../core", default-features = false }
 sp-runtime = { path = "../runtime", default-features = false }
-sp-std = { path = "../std", default-features = false }
 
 [features]
 default = ["std"]
@@ -32,7 +31,6 @@ std = [
 	"sp-application-crypto/std",
 	"sp-core/std",
 	"sp-runtime/std",
-	"sp-std/std",
 ]
 
 # Serde support without relying on std features.

substrate/primitives/test-primitives/src/lib.rs

@@ -19,14 +19,16 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
+extern crate alloc;
+
 use codec::{Decode, Encode};
 
 pub use sp_application_crypto;
 use sp_application_crypto::sr25519;
 
+use alloc::vec::Vec;
 pub use sp_core::{hash::H256, RuntimeDebug};
 use sp_runtime::traits::{BlakeTwo256, Extrinsic as ExtrinsicT, Verify};
-use sp_std::vec::Vec;
 
 /// Extrinsic for test-runtime.
 #[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug, scale_info::TypeInfo)]