put TryInto and TryFrom in sp_std::prelude (#10183)

* Switch to Rust 2021

* Update trybuild to fix errors

* half baked

* fix

* remove unused import

* remove more warnings

Co-authored-by: Bastian Köcher <info@kchr.de>

substrate/frame/democracy/src/conviction.rs

@@ -24,7 +24,7 @@ use sp_runtime::{
 	traits::{Bounded, CheckedDiv, CheckedMul, Zero},
 	RuntimeDebug,
 };
-use sp_std::{convert::TryFrom, result::Result};
+use sp_std::{prelude::*, result::Result};
 
 /// A value denoting the strength of conviction of a vote.
 #[derive(Encode, Decode, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, RuntimeDebug, TypeInfo)]

substrate/frame/democracy/src/tests/lock_voting.rs

@@ -18,7 +18,6 @@
 //! The tests for functionality concerning locking and lock-voting.
 
 use super::*;
-use std::convert::TryFrom;
 
 fn aye(x: u8, balance: u64) -> AccountVote<u64> {
 	AccountVote::Standard {

substrate/frame/democracy/src/vote.rs

@@ -24,7 +24,7 @@ use sp_runtime::{
 	traits::{Saturating, Zero},
 	RuntimeDebug,
 };
-use sp_std::{convert::TryFrom, prelude::*, result::Result};
+use sp_std::prelude::*;
 
 /// A number of lock periods, plus a vote, one way or the other.
 #[derive(Copy, Clone, Eq, PartialEq, Default, RuntimeDebug)]