Drop focal platform job and support

This was dropped in tempest, too[0], and we want to focus on getting and
keeping the jammy job stable.

Still retaining the nodeset definitions until we are sure they are not
needed in other projects.

[0] https://review.opendev.org/c/openstack/tempest/+/884952

Change-Id: Iafb5a939a650b763935d8b7ce7069ac4c6d9a95b

.zuul.yaml

@@ -744,13 +744,6 @@
     vars:
       configure_swap_size: 4096
 
-- job:
-    name: devstack-platform-ubuntu-focal
-    parent: tempest-full-py3
-    description: Ubuntu 20.04 LTS (focal) platform test
-    nodeset: openstack-single-node-focal
-    timeout: 9000
-
 - job:
     name: devstack-platform-ubuntu-jammy-ovn-source
     parent: devstack-platform-ubuntu-jammy
@@ -946,7 +939,6 @@
         - devstack-platform-debian-bookworm
         - devstack-platform-debian-bullseye
         - devstack-platform-rocky-blue-onyx
-        - devstack-platform-ubuntu-focal
         - devstack-platform-ubuntu-jammy-ovn-source
         - devstack-platform-ubuntu-jammy-ovs
         - devstack-platform-openEuler-22.03-ovn-source
@@ -995,7 +987,6 @@
         - devstack
         - devstack-ipv6
         - devstack-platform-debian-bullseye
-        - devstack-platform-ubuntu-focal
         - devstack-platform-rocky-blue-onyx
         - devstack-enforce-scope
         - devstack-multinode

stack.sh

@@ -230,7 +230,7 @@ write_devstack_version
 
 # Warn users who aren't on an explicitly supported distro, but allow them to
 # override check and attempt installation with ``FORCE=yes ./stack``
-SUPPORTED_DISTROS="bookworm|bullseye|focal|jammy|rhel8|rhel9|openEuler-22.03"
+SUPPORTED_DISTROS="bookworm|bullseye|jammy|rhel8|rhel9|openEuler-22.03"
 
 if [[ ! ${DISTRO} =~ $SUPPORTED_DISTROS ]]; then
     echo "WARNING: this script has not been tested on $DISTRO"