media: atomisp: remove hmm_pool_[un]register()

These are no-ops, so lets remove them.

Link: https://lore.kernel.org/linux-media/20220615205037.16549-10-hdegoede@redhat.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>