The IsDocked property has been incorrect for a number of laptops for a
while, as it thought that laptops with hybrid graphics cards were always
docked.

The alternative would have been to use the platform/dock_station
devices, but those are only exported for ACPI docking stations.

Instead, whether an external display is attached (which isn't really
docking) should be checked in the same place where the policy depending
on the value should be applied, such as gnome-settings-daemon.

https://bugs.freedesktop.org/show_bug.cgi?id=36818