Remove XML support from quota and scheduler_hints v3 API plugins

Remove XML support from the following v3 compute API plugins:

 - quota_classes
 - quota_sets
 - scheduler_hints

Part of blueprint remove-v3-xml-api

DocImpact

Change-Id: I3ce2bcb1a7d7e152b0bfb96316ce8f1aab10061d
Merge "Remove XML support from quota and scheduler_hints v3 API plugins"