Revert "Turn off /arch:AVX[2] on Windows builds."

Revert "Turn off /arch:AVX[2] on Windows builds."

This reverts commit c89e2438ae24c862087f8ca1cb076052edbb27ea.

Reason for revert:

I'm going to stub this code out in Chrome instead for now.  Chrome's not going to land something that looks like this, so I'd rather undo it than leave Skia in this odd state.

Original change's description:
> Turn off /arch:AVX[2] on Windows builds.
>
> This canaries a similar change Chrome may need.
>
> BUG=chromium:666707
>
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=5005
>
> Change-Id: Ibf7f9941968d905d865b9be1e63ebbf768870175
> Reviewed-on: https://skia-review.googlesource.com/5005
> Reviewed-by: Mike Klein <mtklein@chromium.org>
> Commit-Queue: Mike Klein <mtklein@chromium.org>
>

TBR=mtklein@chromium.org,brucedawson@chromium.org,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I9562f7877749c61f6ba4d48d6c4b557f09876128
Reviewed-on: https://skia-review.googlesource.com/5069
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>