[media] soc-camera: remove two unused configs

The last users of Kconfig symbols MX3_VIDEO and VIDEO_MX2_HOSTSUPPORT
were removed in v3.2. Their Kconfig entries can be removed now.

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