decl_module! macro: use 'frame_system' instead of system as default ident (#6500)

* Use frame_system as default ident.

* Remove unused 'frame_system' to 'system' renaming.

* Fix construct_runtime_ui tests.

* Rename system to frame_system in sudo/utility pallet test.

* Bump runtime impl_version.

* Update formatting.

Author: shaunxw

src/lib.rs

@@ -112,7 +112,7 @@ use frame_support::{
 	dispatch::{DispatchResult, DispatchResultWithPostInfo},
 	traits::{OnUnbalanced, Currency, Get, Time, Randomness},
 };
-use frame_system::{self as system, ensure_signed, ensure_root};
+use frame_system::{ensure_signed, ensure_root};
 use pallet_contracts_primitives::{RentProjection, ContractAccessError};
 use frame_support::weights::Weight;