HTMLFeatureFieldTest: Set $wgWellFormedXml = true

Bug: 68823
Change-Id: I5e4db4d73a9dfbf30cd54db73e86ef0c6f220d35
Remove unused JS checkbox code

Follow-up to b25446e3b0bc2e95a90e1b8951f9774563ccb354.

Change-Id: I5addcc80a57ab90dcf6d9c52f87aeed06b5be222
Merge "Remove unused JS checkbox code"
Merge "HTMLFeatureFieldTest: Set $wgWellFormedXml = true"