Deprecated transaction.commit/rollback_unless_managed.

Since "unless managed" now means "if database-level autocommit",
committing or rolling back doesn't have any effect.

Restored transactional integrity in a few places that relied on
automatically-started transactions with a transitory API.

django/db/models/deletion.py

@@ -62,8 +62,6 @@ def force_managed(func):
             func(self, *args, **kwargs)
             if forced_managed:
                 transaction.commit(using=self.using)
-            else:
-                transaction.commit_unless_managed(using=self.using)
         finally:
             if forced_managed:
                 transaction.leave_transaction_management(using=self.using)