Remove quota classes extension from the V3 API

As per discussion at the Nova mid cycle meetup the
quota classes extension is being removed from the
V3 API. The extension was apparently part of a larger
body of work the rest of which never managed to merge.
So its not really useful by itself.

Partially implements bp v3-api-remove-extensions

Change-Id: Id1f288baa723df825151bd84aa27089271c2b8e4
Merge "Remove quota classes extension from the V3 API"