qunit: Use sinon sandbox for mediawiki.api.parse.test

This is the last of the mediawiki.api tests that was still making
real requests.

This test had become a parser test for no reason. It is supposed
to test the logic in mediawiki.api.parse which is only:
* making the correct request url
* extract data from response

Change-Id: I9b6eeabe1baa1de7d77623902ef71ba031eb40ac
Merge "qunit: Use sinon sandbox for mediawiki.api.parse.test"