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/session/Cargo.toml

@@ -22,7 +22,6 @@ sp-api = { path = "../api", default-features = false }
 sp-core = { path = "../core", default-features = false }
 sp-runtime = { path = "../runtime", optional = true }
 sp-staking = { path = "../staking", default-features = false }
-sp-std = { path = "../std", default-features = false }
 sp-keystore = { path = "../keystore", optional = true }
 
 [features]
@@ -35,5 +34,4 @@ std = [
 	"sp-keystore/std",
 	"sp-runtime/std",
 	"sp-staking/std",
-	"sp-std/std",
 ]

substrate/primitives/session/src/lib.rs

@@ -19,6 +19,8 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
+extern crate alloc;
+
 use codec::{Decode, Encode};
 
 #[cfg(feature = "std")]
@@ -26,9 +28,9 @@ use sp_api::ProvideRuntimeApi;
 #[cfg(feature = "std")]
 use sp_runtime::traits::Block as BlockT;
 
+use alloc::vec::Vec;
 use sp_core::RuntimeDebug;
 use sp_staking::SessionIndex;
-use sp_std::vec::Vec;
 
 pub mod runtime_api;
 pub use runtime_api::*;

substrate/primitives/session/src/runtime_api.rs

@@ -15,8 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use alloc::vec::Vec;
 pub use sp_core::crypto::KeyTypeId;
-use sp_std::prelude::*;
 
 sp_api::decl_runtime_apis! {
 	/// Session keys runtime api.