media: vimc: stream: remove obsolete function doc

As a more complete version of vimc_streamer_s_streamer comment was added
at "media: vimc: stream: add missing function documentation" commit in
.c file, remove the old documentation from .h file.

Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>