media: soc_camera.h: remove this unused header

The soc_camera driver has been removed and all board files
that used it have been fixed. This header can now be removed
altogether.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>