Drop duplicate sqlalchemy db api methods

Drop duplicate sqlalchemy db api methods

Several methods were redefined at the bottom of
cinder/db/sqlalchemy/api.py. They have been removed:
- quota_get
- quota_get_all_by_project
- quota_create
- quota_update
- quota_destroy
- quota_destroy_all_by_project
- quota_class_get
- quota_class_get_all_by_name
- quota_class_create
- quota_class_update
- quota_class_destroy
- quota_class_destroy_all_by_name
- quota_usage_get
- quota_usage_get_all_by_project
- quota_usage_create
- quota_usage_update
- quota_usage_destroy

Fix bug 1070033

Change-Id: I64b0b0045af7251853da97a8a8c4b2cb09b1dd53