[media] Feature removal: V4L2 selections API target and flag definitions

After unification of the V4L2 and V4L2 subdev selection targets and flags
the old flags are no longer required. Thus they can be removed. However, as
the API is present in a kernel release, this must go through the feature
removal process.

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>