os: don't request read access from CreateFile in Stat

os: don't request read access from CreateFile in Stat

CL 448897 changed os.Stat to request GENERIC_READ access when using
CreateFile to examine a file. This is unnecessary; access flags of 0
will permit examining file metadata even if the file isn't readable.
Revert to the old behavior here.

For #56217

Change-Id: I09220b3bbee304bd89f4a94ec9b0af42042b7773
Reviewed-on: https://go-review.googlesource.com/c/go/+/450296
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>