Move unset_flavor_extra_specs to extra specs file

Flavor unset extra spec schema 'unset_flavor_extra_specs'
is present in flavors.py schema file which should be in
flavors_extra_specs.py file.

Change-Id: Ibea6081129ce05e300b3dc757fabdbed2d3e0570
diff --git a/tempest/lib/services/compute/flavors_client.py b/tempest/lib/services/compute/flavors_client.py
index a699579..2fad0a4 100644
--- a/tempest/lib/services/compute/flavors_client.py
+++ b/tempest/lib/services/compute/flavors_client.py
@@ -205,7 +205,8 @@
         """
         resp, body = self.delete('flavors/%s/os-extra_specs/%s' %
                                  (flavor_id, key))
-        self.validate_response(schema.unset_flavor_extra_specs, resp, body)
+        self.validate_response(schema_extra_specs.unset_flavor_extra_specs,
+                               resp, body)
         return rest_client.ResponseBody(resp, body)
 
     def list_flavor_access(self, flavor_id):