Set confirm_deleted_rows=False to StandardAttribute obj

Do the work of the warning log suggests, since the how many
rows to delete of standardattributes is not an issue to Neutron.
The final goal is to delete them all.

Change-Id: I8113881a2bd2278ce8c912562a172f90e073b686
Closes-Bug: #1916889

neutron_lib/db/standard_attr.py

@@ -68,6 +68,7 @@ class StandardAttribute(model_base.BASEV2):
         # see http://docs.sqlalchemy.org/en/latest/orm/versioning.html for
         # details about how this works
         "version_id_col": revision_number,
+        "confirm_deleted_rows": False,
         "version_id_generator": False  # revision plugin increments manually
     }