Drops unit tests related to fwaas policies.
Tests related to get_firewall_policy/rule are also unnecessary.
They have been migrated to neutron-fwaas already.
Closes-Bug: #1703347
Depends-On: I6dc6b2295a605444c918e44949f4b1485177e82e
Change-Id: Ie866f140fd4e5537ff0d757304ab5279f0cf0a79