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
diff --git a/releasenotes/notes/remove-deprecated-volume-apis-from-v2-volumes-client-cf35e5b4cca89860.yaml b/releasenotes/notes/remove-deprecated-volume-apis-from-v2-volumes-client-cf35e5b4cca89860.yaml
new file mode 100644
index 0000000..12ac5b5
--- /dev/null
+++ b/releasenotes/notes/remove-deprecated-volume-apis-from-v2-volumes-client-cf35e5b4cca89860.yaml
@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    Remove deprecated APIs (``show_pools`` and ``show_backend_capabilities``)
+    from volume v2 volumes_client, and the deprecated APIs are re-realized in
+    volume v2 scheduler_stats_client (``list_pools``) and capabilities_client
+    (``show_backend_capabilities``) accordingly.