Switch to Rust 2021 (#10170)

* Switch to Rust 2021

* Update trybuild to fix errors

substrate/client/rpc/Cargo.toml

@@ -2,7 +2,7 @@
 name = "sc-rpc"
 version = "4.0.0-dev"
 authors = ["Parity Technologies <admin@parity.io>"]
-edition = "2018"
+edition = "2021"
 license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
 homepage = "https://substrate.io"
 repository = "https://github.com/paritytech/substrate/"

substrate/client/rpc/src/chain/mod.rs

@@ -83,8 +83,6 @@ where
 		match number {
 			None => Ok(Some(self.client().info().best_hash)),
 			Some(num_or_hex) => {
-				use std::convert::TryInto;
-
 				// FIXME <2329>: Database seems to limit the block number to u32 for no reason
 				let block_num: u32 = num_or_hex.try_into().map_err(|_| {
 					Error::Other(format!(