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/arithmetic/src/lib.rs

@@ -19,6 +19,8 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
+extern crate alloc;
+
 /// Copied from `sp-runtime` and documented there.
 #[macro_export]
 macro_rules! assert_eq_error_rate {
@@ -49,7 +51,8 @@ pub use per_things::{
 };
 pub use rational::{MultiplyRational, Rational128, RationalInfinite};
 
-use sp_std::{cmp::Ordering, fmt::Debug, prelude::*};
+use alloc::vec::Vec;
+use core::{cmp::Ordering, fmt::Debug};
 use traits::{BaseArithmetic, One, SaturatedConversion, Unsigned, Zero};
 
 use codec::{Decode, Encode, MaxEncodedLen};
@@ -429,7 +432,7 @@ mod normalize_tests {
 mod threshold_compare_tests {
 	use super::*;
 	use crate::traits::Saturating;
-	use sp_std::cmp::Ordering;
+	use core::cmp::Ordering;
 
 	#[test]
 	fn epsilon_ord_works() {