selftests/hid: tablets: remove unused class

Looks like this is a leftover

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Jiri Kosina <jkosina@suse.com>
Link: https://lore.kernel.org/r/20231206-wip-selftests-v2-4-c0350c2f5986@kernel.org


Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>