In change-id Ide2d53caf1bc5e3ba49f34b2f48de31abaf655d0 we removed the
nested quotas, but there are still some leftover code of it in cinder.
This code is useless, and in some cases not cheap, for example the call
to quota_allocated_get_all_by_project we do in every reservation.
This patch removes most of the remaining nested quota code and leaves
the DB structure changes for the next cycle, since removing them now
would break rolling upgrades.
Change-Id: Ibdbef651208c856ed75dd9af4dd711895e212910