Feature: tools: Drop cluster-clean script

Now that the cts script has ben removed, cluster-clean is not
particularly useful, and we don't use it internally.

It:

• Stops/kills cluster services on all nodes. Other high-level tools like pcs and crmsh can do this. (if --kill is used)
• Kills valgrind on all nodes (even if it's running something unrelated to Pacemaker). (if --kill is used)
• Deletes cluster logs and a bunch of system logs that are unrelated to Pacemaker, on all nodes.
• Deletes Pacemaker state and shared memory files on all nodes.
• Deletes all "*.valgrind" files in /tmp on all nodes.
• Restarts rsyslog and the systemd journal on all nodes.

Overall, this option seems overzealous, affecting things that are not
owned by Pacemaker.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>