Remove stable/wallaby job from master gate

stable/wallaby is in EM state. As Tempest and
plugins masters does not support Em stable branches
qa team is pinning tempest in devstack stable/wallaby
tesitng[1]. With that we do not need to test the
stable/wallaby jobs on master gate

[1] https://review.opendev.org/c/openstack/devstack/+/871782

Change-Id: If5db25580fc979f9b4184e3556d2e1f1ed227c6f
1 file changed