dashboard: do different stuff based on appliance type

circle/dashboard/views.py

@@ -2160,7 +2160,10 @@ class DiskRemoveView(DeleteView):
         disk = self.get_object()
         app = disk.get_appliance()
 
-        app.remove_disk(disk=disk, user=request.user)
+        if isinstance(app, Instance):
+            app.remove_disk(disk=disk, user=request.user)
+        else:  # isinstance(app, InstanceTemplate)
+            app.disks.remove(disk)
         disk.destroy()
 
         next_url = request.POST.get("next")