time: make time.Until a few nanoseconds faster

time: make time.Until a few nanoseconds faster

This is similar to CL 518336.

For #61765.

Change-Id: I7c1d92a3b3e2b6c1c0058a2094997d93082ad139
Reviewed-on: https://go-review.googlesource.com/c/go/+/521237
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>