Remove deprecated volume apis from v2 volumes client

The APIs 'show_pools' and 'show_backend_capabilities' in v2
volumes_client are deprecated, and they are re-realized in volume
v2 scheduler_stats_client and capabilities_client. Now these two
deprecated APIs are not being used by any other projects, and it is
time to remove them from the v2 volumes_client.

Change-Id: Iaed636bffe912e424dbccb20c38946525af052db
2 files changed