[media] media: Documentation: remove V4L2_FL_USE_FH_PRIO flag

The V4L2_FL_USE_FH_PRIO has been removed from the code, now remove it from the
documentation.

Signed-off-by: Ramakrishnan Muthukrishnan <ramakrmu@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>