Partial revert of Enable MSVC warning C4018 for various directories that seem to pass as-is.

Partial revert of Enable MSVC warning C4018 for various directories that seem to pass as-is. (patchset #2 id:20001 of https://codereview.chromium.org/1246863002/)

Reason for revert:
Got a signed/unsigned mismatch warning on GPU Win Builder
(gtffixedtestvertexorder.c:58).

Reverting change to gles2_conform_test.gyp; other files not reverted.

Original issue's description:
> Enable MSVC warning C4018 for various directories that seem to pass as-is.
>
> BUG=398202
> TEST=none
> TBR=brettw
>
> Committed: https://crrev.com/513df87e8724587dc7be0d27a5f79652275c0767
> Cr-Commit-Position: refs/heads/master@{#339602}

TBR=brettw@chromium.org,pkasting@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=398202
Committed: https://crrev.com/2e73278918aeab1d0f4d028e48d8ba85a1b0c8c1
Cr-Commit-Position: refs/heads/master@{#339606}

[Matt Giuca, 2015-07-21 03:13:42]

Created Revert of Enable MSVC warning C4018 for various directories that seem to
pass as-is.

[commit-bot: I haz the power, 2015-07-21 03:13:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1242333005/1

[Matt Giuca, 2015-07-21 03:14:04]

The CQ bit was unchecked by mgiuca@chromium.org

[commit-bot: I haz the power, 2015-07-21 03:14:11]

The CQ bit was unchecked by commit-bot@chromium.org

[Matt Giuca, 2015-07-21 03:19:19]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2015-07-21 03:19:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1242333005/120001

[commit-bot: I haz the power, 2015-07-21 03:20:00]

Committed patchset #2 (id:120001)

[commit-bot: I haz the power, 2015-07-21 03:20:57]

Patchset 2 (id:??) landed as
https://crrev.com/2e73278918aeab1d0f4d028e48d8ba85a1b0c8c1
Cr-Commit-Position: refs/heads/master@{#339606}