compositor: Default to META_SYNC_DELAY == 0
The purpose of sync_delay is to reduce latency. However it only works if the machine is consistently fast enough to render in much less than the refresh interval. So for fast machines the benefit was a 2ms reduction in latency; not that noticeable.
For slow machines, using a sync_delay could hurt quite a bit. Such machines that can't render in (interval-2)ms [actually a bit less because kernel page flipping occupies a couple of milliseconds too]. So they would miss the deadline more often - effectively halving the framerate and increasing latency by 16ms.
So on averages using a sync_delay hurts performance more than it helps.