win: Stop passing /wd4206 in PCH builds.

We already don't pass it for blink's PCHs and it seems to work fine there.
No intended behavior change, please revert if this breaks you.

BUG=none

Review-Url: https://codereview.chromium.org/2830733006
Cr-Original-Commit-Position: refs/heads/master@{#467353}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d7119231dcd23626b491d050706871c2729601a3
1 file changed