media: vb2: drop VB2_BUF_STATE_REQUEUEING

The last user of this state has been converted, so we can now drop
this. Requeueing causes the queue to become unordered, which causes
problems with requests and (in the future) fences.

Since it is no longer needed, just get rid of this.

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