media: cx25821: remove cx25821-audio-upstream.c and cx25821-video-upstream.c

Those two files are unused since commit 486a7a28 ("[media] cx25821: remove cx25821-audio-upstream.c")
and commit b6f21dc3 ("[media] cx25821: remove video output support")
Remove them from tree.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>