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.

substrate/frame/offences/src/lib.rs

@@ -37,7 +37,6 @@ use sp_staking::{
 	offence::{Offence, ReportOffence, Kind, OnOffenceHandler, OffenceDetails, OffenceError},
 };
 use codec::{Encode, Decode};
-use frame_system as system;
 
 /// A binary blob which represents a SCALE codec-encoded `O::TimeSlot`.
 type OpaqueTimeSlot = Vec<u8>;