Remove or weaken hints about "effective resolution of sleep delays is 10 ms"?

Hi,

Several places in our docs have blurbs like
> Note that on many systems, the effective resolution of sleep delays is
> 10 milliseconds; setting wal_writer_delay</> to a value that
> is not a multiple of 10 might have the same results as setting it to
> the next higher multiple of 10.
Afaik that's not the case on any recent operating system/hardware. So
perhaps we should just remove all of those blurbs, or just replace them
with something like "on some older systems the effective resolution of
sleep delays is limited to multiples of 10 milliseconds"?

Greetings,

Andres Freund