[media] V4L: tw9910: remove a not really implemented cropping support

Cropping is not really correctly implemented by this driver and only
needlessly obfuscates the code. Remove it.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>