core: Reduce video update queueing.

A video update frame is used to indicate that a channel
with video negotiated should provide a full frame so the
decoder decoding the stream is able to do so. In situations
where a queue is used to store frames it makes no sense
for the queue to contain multiple video update frames. One
is sufficient to have a full frame be sent.

ASTERISK-27222

Change-Id: Id3f40a6f51b740ae4704003a1800185c0c658ee7