This commit drops magnum-functional-api (which uses legacy-dsvm-base due
to be removed in the V cycle) in favour of
magnum-tempest-plugin-tests-api defined in the magnum-tempest-plugins
repo (which uses the new devstack-tempest job recommended for running
Tempest tests in Zuul v3) for API Tempest tests.
Story: 2007561
Task: 39443
Depends-On: https://review.opendev.org/#/c/721077/
Change-Id: I91446f8773ecec1286c9913c3fff688bd8d9a087
76502dd57d