Addressed comments

Author: davidz627

csi.proto

@@ -555,13 +555,7 @@ message NodeStageVolumeRequest {
   map<string,string> volume_attributes = 7;
 }
 
-message NodeStageVolumeResponse {
-  // The SP specific information that will be passed to the Plugin in
-  // the subsequent `NodePublishVolume` calls
-  // for the given volume.
-  // This information is opaque to the CO. This field is OPTIONAL.
-  map<string, string> publish_volume_info = 1;
-}
+message NodeStageVolumeResponse {}
 ////////
 ////////
 message NodeUnstageVolumeRequest {