Clean up removed hacking rule from [flake8] ignore lists

We bump hacking>=0.10.0, and hacking removed some rules, for
the full list of rules please see [1]. So don't need them any more.

Hacking related commits:
Remove H904 in commit b1fe19ebebe47a36b905d709467f5e82521bbd96
Add H105 using author tags
Add H238 hacking no old style class
Add H501 hacking no locals
[1]https://github.com/openstack-dev/hacking/blob/master/setup.cfg#L30

Change-Id: I6a1f3c3ef22be0962ffb81a5da5660837552e5d7
diff --git a/manila_tempest_tests/tests/api/admin/test_scheduler_stats.py b/manila_tempest_tests/tests/api/admin/test_scheduler_stats.py
index 576e499..973e52e 100644
--- a/manila_tempest_tests/tests/api/admin/test_scheduler_stats.py
+++ b/manila_tempest_tests/tests/api/admin/test_scheduler_stats.py
@@ -140,4 +140,4 @@
         self.assertEmpty(pool_list)
 
     def _wrap_regex_for_exact_match(self, regex):
-        return '^%s$' % regex
\ No newline at end of file
+        return '^%s$' % regex