runtime: don't use atomic store in noteclear on AIX
In CL 163624 we added an atomic store in noteclear on AIX only.
In the discussion on issue #63384 we think we figured out that the
real problem was in the implementation of compare-and-swap on ppc64.
That is fixed by CL 533118, so the atomic store is no longer required.
For #30189
For #63384
Change-Id: I60f4f2fac75106f2bee51a8d9663259dcde2029c
Reviewed-on: https://go-review.googlesource.com/c/go/+/534517
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> Reviewed-by: Joel Sing <joel@sing.id.au>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>