Invoke the "crontab" removal command using a list (DBTS: #940577)
This PR does the work of removing the crontab file for a user safely.
It does this by using a list for the /usr/bin/crontab sub-command instead of a string.
It does have a deficiency of adding STDERR output to any deluser command where the user does not have a crontab file (which is the norm). This will need to be fixed, likely, on the crontab side of things.
Note that this fix attempts to be minimally invasive due to the security implications. Many other improvements are possible in how we clean up during account deletion.
Edited by deadjoe