Revert "rtpjitterbuffer: If we have an immediate timeout, don't try to find an earlie...

Revert "rtpjitterbuffer: If we have an immediate timeout, don't try to find an earlier timeout"

This reverts commit 0c21cd7177ea883c710999147ddcedb19004d182.

If we have multiple immediate timers, we want to first handle the one with the
lowest sequence number... which would be broken now.

Instead of this we should just use a GSequence for the timers, and have them
sorted first by timestamp, and for equal timestamps by sequence number. Then
we would always only have to take the very first timer from the list and never
have to look at any others.