Drop DEVSTACK_GATE_FEATURE_MATRIX

DEVSTACK_GATE_FEATURE_MATRIX seems to be an old legacy thing that
is no longer being used.  It currently prevents using the jobs in
openstack/devstack without adding openstack/devstack-gate for the
role.

Change-Id: Iab9b4862c01043d2c158398bac4b3b289a0adba0

Author: mnaser

doc/source/zuul_ci_jobs_migration.rst

@@ -195,12 +195,6 @@ value defined in the parent job, or the default from DevStack, if any.
      - A bridge called br-infra is set up for all jobs that inherit
        from multinode with a dedicated `bridge role
        <https://zuul-ci.org/docs/zuul-jobs/general-roles.html#role-multi-node-bridge>`_.
-   * - DEVSTACK_GATE_FEATURE_MATRIX
-     - devstack-gate
-     - ``test_matrix_features`` variable of the test-matrix role in
-       devstack-gate. This is a temporary solution, feature matrix
-       will go away. In the future services will be defined in jobs
-       only.
    * - DEVSTACK_CINDER_VOLUME_CLEAR
      - devstack
      - *CINDER_VOLUME_CLEAR: true/false* in devstack_localrc in the

playbooks/pre.yaml

@@ -26,7 +26,6 @@
       set_fact:
         external_bridge_mtu: "{{ local_mtu | int - 50 }}"
   roles:
-    - test-matrix
     - configure-swap
     - setup-stack-user
     - setup-tempest-user