Remove unused methods from XhrMethods

Closes #143

What does this MR do?

Removes different methods inside XhrMethods.php, the giant behind xhr.php?f= which are unused.

How confident are you it won't break things if deployed?

quite

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))