media: vimc: common: remove unused function 'vimc_pipeline_s_stream'

The function 'vimc_pipeline_s_stream' is not used and can be
removed.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>