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/support/src/error.rs

@@ -47,7 +47,7 @@ pub use frame_metadata::{ModuleErrorMetadata, ErrorMetadata, DecodeDifferent};
 ///     }
 /// }
 ///
-/// # use frame_system::{self as system, Trait};
+/// # use frame_system::Trait;
 ///
 /// // You need to register the error type in `decl_module!` as well to make the error
 /// // exported in the metadata.