Remove Extended maintainance stable branch job from master gate

stable/queens and stable/rocky are in extended maintainance state
and devtack use the older Tempest version to tests them not the master.

Testing them on master gate is not needed as heat-tempest-plugin master
cannot support testing them due to python required version for plugin
and Tempest. Even we test them on master gate, they run with older Tempest
so they are not actually testing the master code against those stable.

We can continue testing the supported stable branch where master Tempest and
plugins are used.

Same is done Tempest and other plugins side:
- https://review.opendev.org/#/c/722183/
- https://review.opendev.org/#/c/707111/

Change-Id: I3dd3c354947461ba65906251fb42897b0b8ce6f5
1 file changed