Remove multinode legacy gate
Remove multinode legacy gate

This patch set removes the legacy multinode gates as those are
being transitioned to zuul v3, and the legacy multinode gates have high
rate of failure.  The single nodes will remain a while longer as a sanity
check until the new gates are fully functional.

Change-Id: Ie8f685eb2737c91d37c670db24d877e7efbfe0f2

openstack-infra/project-config,openstack-infra/project-config