Fixed #19720 -- Oracle ordering related delete regression

When a query had a complex where condition (a condition targeting more
than the base table) a subquery was used for deletion. However, the
query had default ordering from the model's meta and Oracle doesn't
work with ordered subqueries.

The regression was caused by fast-path deletion code introduced in
1cd6e04cd4 for fixing #18676.

Thanks to Dylan Klomparens for the report.

django/db/models/query.py

@@ -539,7 +539,7 @@ class QuerySet(object):
         # Disable non-supported fields.
         del_query.query.select_for_update = False
         del_query.query.select_related = False
-        del_query.query.clear_ordering()
+        del_query.query.clear_ordering(force_empty=True)
 
         collector = Collector(using=del_query.db)
         collector.collect(del_query)