BUG: Module.Submodule does not get dead_code removed, but Module does.

[jaeh]

Fix:
src/lib/babel has a dead_code removal function, which does not detect Module.SubModule after it removed Module.

This is a bug if a @magic-modules is installed and then not used in the pages.

fix: only parse the used and unused tags in dead_code, pass them back, then remove them in one step, together with CHECK_PROPS.

this will also allow removal of actions, effects, subscriptions, libraries and other dead code that the default dead code elimination and treeshaking can not detect.