Remove the nodeset "devstack-single-node-opensuse-15"

The nodepool "opensuse-15" is no longer available since [1].

[1]https://review.opendev.org/c/openstack/project-config/+/955214

Signed-off-by: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Change-Id: I0c48ee0b7daded1f10eda5861ae1ac0bcedd168c

.zuul.yaml

@@ -48,16 +48,6 @@
         nodes:
           - controller
 
-- nodeset:
-    name: devstack-single-node-opensuse-15
-    nodes:
-      - name: controller
-        label: opensuse-15
-    groups:
-      - name: tempest
-        nodes:
-          - controller
-
 - nodeset:
     name: devstack-single-node-debian-bookworm
     nodes: