Bug#883487: mate-system-monitor: Don't recommend libgksu2-0

[Jeremy Bicha]

Package: mate-system-monitor
Version: 1.18.1-1
Severity: important
Tags: buster

mate-system-monitor recommends libgksu2-0. However, the Debian GNOME
team would like to remove libgksu from Debian. According to the
upstream change log, that dependency can be replaced by
/usr/bin/pkexec (provided by the policykit-1 package in Debian).

https://github.com/mate-desktop/mate-system-monitor/blob/master/NEWS

Thanks,
Jeremy Bicha