Split mediawiki.toolbar from mediawiki.action.edit

Follows-up 285c52039bf4d2f9b.

Get rid of mediawiki.mediawiki.action.toolbar. Not keeping a
backwards-compat alias since this module is not supposed to be used
publicly in its current form.

Change-Id: I403216c6916e1f4d29216a55c3fe6c92eb68400b
Merge "Split mediawiki.toolbar from mediawiki.action.edit"