mediawiki.language: Combine with 'mediawiki.language.data' and 'mediawiki.language...

mediawiki.language: Combine with 'mediawiki.language.data' and 'mediawiki.language.init'

The latter two modules are never used separately and have no references
anywhere in Wikimedia Git outside MediaWiki core.

Remove without deprecation as they were introduced only as internal
work-around to be able to call setData after init.js and the rest of
'mediawiki.language'. Which is actually trivially done by concatenating
one after the other, but for some reason I didn't think of that when
reviewing 4c6c50f20661 in 2012.

Also fix an annoying race condition in the unit tests that
often caused tests to fail locally.

Change-Id: Ic61f86b0dcbfac82da230770f66cb72e97bd9a03