Delete the useless code

These lines of code are not used anywhere, and we already have a
command "gnocchi resource-type list".

Change-Id: Ia14f4da3bb6d2bdf19b8cb0efc2df9c7adbe68a8

gnocchiclient/v1/resource.py

@@ -167,7 +167,3 @@ class ResourceManager(base.Manager):
         return self._post(
             url, headers={'Content-Type': "application/json"},
             data=jsonutils.dumps(query)).json()
-
-    def list_types(self):
-        """List the resource types supported by gnocchi"""
-        return self._get(self.url).json()