ACPI / dock: Drop remove_dock_dependent_devices()

Since remove_dock_dependent_devices() is only called from acpi_dock_add()
and it only is called if the add_dock_dependent_device() adding the
dock station to its own list of dependent devices has failed, it is not
really necessary, because the dock station's list of dependent devices
is guaranteed to be empty at that point.  Drop it, then.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>