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/contracts/src/benchmarking/code.rs

@@ -36,7 +36,7 @@ use pwasm_utils::parity_wasm::{
 use sp_core::crypto::UncheckedFrom;
 use sp_runtime::traits::Hash;
 use sp_sandbox::{EnvironmentDefinitionBuilder, Memory};
-use sp_std::{borrow::ToOwned, convert::TryFrom, prelude::*};
+use sp_std::{borrow::ToOwned, prelude::*};
 
 /// Pass to `create_code` in order to create a compiled `WasmModule`.
 ///

substrate/frame/contracts/src/benchmarking/mod.rs

@@ -44,7 +44,7 @@ use sp_runtime::{
 	traits::{Bounded, Hash},
 	Perbill,
 };
-use sp_std::{convert::TryInto, default::Default, vec, vec::Vec};
+use sp_std::prelude::*;
 
 /// How many batches we do per API benchmark.
 const API_BENCHMARK_BATCHES: u32 = 20;