Remove unused methods from volumes_client

Since I59e88344e83b8c0665a04c8ef55126a8f27bbf57 , these methods have
become unused and that was over 2 years ago. So we don't test these
APIs over 2 years.
Then this patch removes these methods before defining stable interfaces.

Partially implements blueprint consistent-service-method-names

Change-Id: I0f8f16430de3fb51a02e97f19b44d983072ae15a
1 file changed