MAINTAINERS: remove staging sections

Two commits moved files from staging to drivers/media/

commit d6ce55de ("[media] move cx25821 out of staging")
commit be304970

 ("[media] move tm6000 to drivers/media/video")

Remove the sections.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>