ZTS: Remove functional tests via matrix

This commit changes the workflow of the github actions.

- Ubuntu 20.04, 22.04, 24.04 will be tested via QEMU now
- remove unused scripts of this commit: b7bc334d1
- re-add the zloop standalone testings via zloop.yml

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #16549

.github/workflows/scripts/qemu-3-deps.sh

@@ -141,6 +141,10 @@ case "$1" in
     ;;
 esac
 
+# This script is used for checkstyle + zloop deps also.
+# Install only the needed packages and exit - when used this way.
+test -z "${ONLY_DEPS:-}" || exit 0
+
 # Start services
 echo "##[group]Enable services"
 case "$1" in