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/grandpa/src/lib.rs

@@ -43,7 +43,7 @@ use frame_support::{
 	decl_error, decl_event, decl_module, decl_storage, storage, traits::KeyOwnerProofSystem,
 	Parameter,
 };
-use frame_system::{self as system, ensure_signed, DigestOf};
+use frame_system::{ensure_signed, DigestOf};
 use sp_runtime::{
 	generic::{DigestItem, OpaqueDigestItemId},
 	traits::Zero,