Disable desk dock apps.

When a device is attached to a desk dock, the
CATEGORY_DESK_DOCK intent will no longer be fired.
As a side effect, the "dock home" behavior (which captures
the home key for the dock app as long as the device is
docked) is now disabled for desk docks.

Car docks are unchanged.

Bug: 5591015
Change-Id: I7884f655913c31cf53b88cb2e2b371987be27f64