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

@@ -78,7 +78,7 @@ use frame_support::{
 	traits::{Currency, ReservableCurrency, OnUnbalanced, Get, BalanceStatus, EnsureOrigin},
 	weights::Weight,
 };
-use frame_system::{self as system, ensure_signed};
+use frame_system::ensure_signed;
 
 mod benchmarking;