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
diff --git a/stack.sh b/stack.sh
index a8f46bf..c8810cd 100755
--- a/stack.sh
+++ b/stack.sh
@@ -230,7 +230,7 @@
 
 # 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"