resourceloader: Remove mwLoadEnd code (moved to Navigation Timing)

resourceloader: Remove mwLoadEnd code (moved to Navigation Timing)

This internal hook was primarily added for the Navigation Timing
extension. As part of T192623, this should be removed from mediawiki.js
because:

* It is not used in anyway by core.
* It should not be used by anything other than Navigation Timing.
* It depends heavily on jQuery, which we don't want for mediawiki.js.

Bug: T192623
Depends-On: I011c9d1beebe6fa8d21ab9260da0a817ff7aa5f0
Change-Id: I0bf60d37ebea96f2a22044f9db221c87dd88521c