Remove quota-class subcommand

quota-classes API was already removed.
  Change-Id: I1110022d6f628d03aaf363da707f2d2ef1600437
This patch removed quota-class subcommand from nova client.

Change-Id: I18bf7c255fabdb52c8ce8159f68c3e5c70e54993
Merge "Remove quota-class subcommand"