Fix the broken weight multiplier update function (#6334)

* Initial draft, has some todos left

* remove ununsed import

* Apply suggestions from code review

* Some refactors with migration

* Fix more test and cleanup

* Fix for companion

* Apply suggestions from code review

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update bin/node/runtime/src/impls.rs

* Fix weight

* Add integrity test

* length is not affected.

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

substrate/frame/system/src/lib.rs

@@ -570,7 +570,7 @@ decl_module! {
 		/// A dispatch that will fill the block weight up to the given ratio.
 		// TODO: This should only be available for testing, rather than in general usage, but
 		// that's not possible at present (since it's within the decl_module macro).
-		#[weight = (*_ratio * T::MaximumBlockWeight::get(), DispatchClass::Operational)]
+		#[weight = *_ratio * T::MaximumBlockWeight::get()]
 		fn fill_block(origin, _ratio: Perbill) {
 			ensure_root(origin)?;
 		}