Revert "morebits.date: Don't import methods that collide with PageTriage (T268513)"

[siddharthvp]

This reverts commit c6f2bd4f3809e3f59124949d31c791923d4a93f1.

The linked phab task has been resolved now - PageTriage is no longer using date.js external which messes up Date.prototype.

[NovemLinguae]

@siddharthvp. What's the easiest way to manually test this? Perhaps a test case that was broken before the old patch?

[siddharthvp]

This is a no-op now since the MediaWiki changes have been merged. So this is just code simplification - doesn't require testing per se (other than to check Morebits.date is not broken 😅).