Move editoptions styling to mediawiki.skinning/interface.css

Move editoptions styling to mediawiki.skinning/interface.css

Adding the editoptions box styling to mediawiki.skinning.interface instead
of the skin-agnostic mediawiki.action.* means it will only be added to skins
where it's likely to be appropriate, as this is also where the similar styles
for toc, categories, etc are defined.

This way skins in which the editoptions box would be inappropriate need never
worry about it anyway because they won't be using mediawiki.skinning.interface
for the same reason.

Bug: 58254
Change-Id: Ibd1c0617c426e34e7213ca0ce89a126340b012a7