Unset all globals unneeded for unit tests, assert correct directory

* Unset globals to avoid tests that look like unit tests but actually rely on
  globals
* move some tests out of unit directory so that the test suite will pass.
* Assert that tests which extend MediaWikiUnitTestCase are in a directory with
  "/unit/" in its path name

Depends-On: I67b37b1bde94eaa3d4298d9bd98ac57995ce93b9
Depends-On: I90921679518ee95fe393f8b1bbd9134daf0ba032
Bug: T87781
Change-Id: I16691fc8ac063705ba0c2bc63b96c4534ca8660b