changeset 04934e44e3784a1b969582e2d59afcec278470c6 removed the last implementation
that were still using the V4L1 obsoleted header.
Now, video_decoder.h is not used anymore by any driver.

Let's remove it and all references for it in Kernel.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>