HID: primax: Remove px_probe() and px_remove() functions

The px_probe() and px_remove() functions do not have any special initialization
and cleanup. Remove them and let HID core handle the default probe/remove
actions.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>