Drop lower constraints testing

Projects like oslo are dropping lower constraints
testing. There is also discussion to drop it until
we find a proper setup. For details, please follow
the ML thread. TC will have updates soon.

http://lists.openstack.org/pipermail/openstack-discuss/2021-January/019679.html

story: 2008482
task: 41523

Addionally in train, cap bandit.
Similar to https://review.opendev.org/c/openstack/nova/+/766171



Drop releasenote jobs from check and gate.

Change-Id: Ia91451c0f93ffe4c7a555874f8f843e01b146df5
Signed-off-by: Spyros Trigazis <spyridon.trigazis@cern.ch>
(cherry picked from commit 2fa68f12)