Three autostarted desktop services are failing to start in the
gnome-flashback desktop manager service, leaving warnings in the log:
gnome-flashback-clipboard
gnome-flashback-idle-monitor
gnome-flashback-media-keys
Fix by only remove $out/libexec/gnome-flashback-metacity (which is
still not useful since we implement that ourselves) instead of the
entire $out/libexec.
The consequence of gnome-flashback-idle-monitor not running is that
the desktop manager does not get the message that the system is idle,
so the screen never dims or locks.
17c59fd8d5