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
diff --git a/tempest/services/volume/base/base_volumes_client.py b/tempest/services/volume/base/base_volumes_client.py
index 273dbbb..8130089 100755
--- a/tempest/services/volume/base/base_volumes_client.py
+++ b/tempest/services/volume/base/base_volumes_client.py
@@ -218,22 +218,6 @@
         self.expected_success(202, resp.status)
         return rest_client.ResponseBody(resp, body)
 
-    def volume_begin_detaching(self, volume_id):
-        """Volume Begin Detaching."""
-        # ref cinder/api/contrib/volume_actions.py#L158
-        post_body = json.dumps({'os-begin_detaching': {}})
-        resp, body = self.post('volumes/%s/action' % volume_id, post_body)
-        self.expected_success(202, resp.status)
-        return rest_client.ResponseBody(resp, body)
-
-    def volume_roll_detaching(self, volume_id):
-        """Volume Roll Detaching."""
-        # cinder/api/contrib/volume_actions.py#L170
-        post_body = json.dumps({'os-roll_detaching': {}})
-        resp, body = self.post('volumes/%s/action' % volume_id, post_body)
-        self.expected_success(202, resp.status)
-        return rest_client.ResponseBody(resp, body)
-
     def create_volume_transfer(self, **kwargs):
         """Create a volume transfer.