rate: extend maximum-delay slop to all platforms
rate: extend maximum-delay slop to all platforms

I initially added some timing slop for specific platforms based on the
failures we had seen so far (and a theory explaining at least some of
those failures). But now we've seen overruns on other platforms too,
so perhaps we should use the same factors everywhere.

Fixes #43055 (I hope).

Change-Id: Ib6035b55acd9d17acc7ad78065abf5f1e3f9dfe7
Reviewed-on: https://go-review.googlesource.com/c/time/+/399535
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

golang/time