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/uniques/src/impl_nonfungibles.rs

@@ -23,7 +23,7 @@ use frame_support::{
 	BoundedSlice,
 };
 use sp_runtime::{DispatchError, DispatchResult};
-use sp_std::convert::TryFrom;
+use sp_std::prelude::*;
 
 impl<T: Config<I>, I: 'static> Inspect<<T as SystemConfig>::AccountId> for Pallet<T, I> {
 	type InstanceId = T::InstanceId;

substrate/frame/uniques/src/tests.rs

@@ -21,7 +21,7 @@ use super::*;
 use crate::mock::*;
 use frame_support::{assert_noop, assert_ok, traits::Currency};
 use pallet_balances::Error as BalancesError;
-use sp_std::convert::TryInto;
+use sp_std::prelude::*;
 
 fn assets() -> Vec<(u64, u32, u32)> {
 	let mut r: Vec<_> = Account::<Test>::iter().map(|x| x.0).collect();