Revert "Use fernet in gates"

We have pin keyston to queens release which supports UUID token through
https://review.openstack.org/546475, let us use UUID in queens and
migrate to fernet in rocky cycle.

This reverts commit df0bf190.

Change-Id: Ifb0112315b5047461ce0bf02c754cc0beac52d9a

tests/templates/globals-default.j2

@@ -36,5 +36,3 @@ enable_cinder: "yes"
 ceph_pool_pg_num: 64
 ceph_pool_pgp_num: 64
 {% endif %}
-
-keystone_token_provider: "fernet"