Drop legacy scenario multinode job from Tempest

The legacy job:
legacy-tempest-dsvm-neutron-scenario-multinode-lvm-multibackend
has been superseded by https://review.openstack.org/#/c/580877/5
which uses ZuulV3.

So we should drop this job to reduce unnecessary consumption of
nodes.

Change-Id: I5b8df4f521cd3118fa26cbb4397e6d4f18133684

zuul.d/projects.yaml

@@ -14144,17 +14144,6 @@
               - ^setup.cfg$
               - ^tempest/hacking/.*$
               - ^tempest/tests/.*$
-        - legacy-tempest-dsvm-neutron-scenario-multinode-lvm-multibackend:
-            voting: false
-            irrelevant-files:
-              - ^(test-|)requirements.txt$
-              - ^.*\.rst$
-              - ^doc/.*$
-              - ^etc/.*$
-              - ^releasenotes/.*$
-              - ^setup.cfg$
-              - ^tempest/hacking/.*$
-              - ^tempest/tests/.*$
         - openstack-tox-cover:
             voting: false
         - tempest-full: