Remove legacy-tempest-dsvm-cinder-v1

Since https://review.openstack.org/#/c/573135/ there's no support in
Tempest for Cinder v1 testing, thus remove obsolete experimental job
legacy-tempest-dsvm-cinder-v1.

Change-Id: I5c512c02bcee0244703e2fe117958fa3cc31dc13
diff --git a/.zuul.yaml b/.zuul.yaml
index 9569a55..677ecfa 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -398,8 +398,6 @@
             irrelevant-files: *tempest-irrelevant-files
         - legacy-tempest-dsvm-lvm-multibackend:
             irrelevant-files: *tempest-irrelevant-files
-        - legacy-tempest-dsvm-cinder-v1:
-            irrelevant-files: *tempest-irrelevant-files
         - devstack-plugin-ceph-tempest-py3:
             irrelevant-files: *tempest-irrelevant-files
         - legacy-tempest-dsvm-neutron-pg-full: