cmd/go/internal/modload: remove aix from stat_openfile.go comment
cmd/go/internal/modload: remove aix from stat_openfile.go comment

syscall.Access is supported and used on aix since CL 263540.

Change-Id: Ie50cc3da68b49b22d622d94faec0231c52502037
Reviewed-on: https://go-review.googlesource.com/c/go/+/396374
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go