Revert of Add a GN flag for the Windows multi-dll build.

Revert of Add a GN flag for the Windows multi-dll build. (patchset #3 id:40001 of https://codereview.chromium.org/1120803003/)

Reason for revert:
May have caused some link errors on windows: https://build.chromium.org/p/chromium.win/builders/Win%20x64%20GN/builds/814

Original issue's description:
> Add a GN flag for the Windows multi-dll build.
>
> The first pass of moving the other Chrome-specific build flags out of the root build config file and into the new one. This requires both ffmpeg and Blink changes to finish landing.
>
> R=scottmg@chromium.org
> TBR=ddorwin@chromium.org (widevine)
>
> Committed: https://crrev.com/edff53a35780ba2f515c7e8d4f7131c91151e1a3
> Cr-Commit-Position: refs/heads/master@{#327854}

TBR=scottmg@chromium.org,brettw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/e203954b33d80072a7c8d256ffdc69fa42262765
Cr-Commit-Position: refs/heads/master@{#327861}

[rickyz (no longer on Chrome), 2015-05-01 01:43:40]

Created Revert of Add a GN flag for the Windows multi-dll build.

[commit-bot: I haz the power, 2015-05-01 01:43:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1117063004/1

[commit-bot: I haz the power, 2015-05-01 01:45:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-01 01:46:18]

Patchset 1 (id:??) landed as
https://crrev.com/e203954b33d80072a7c8d256ffdc69fa42262765
Cr-Commit-Position: refs/heads/master@{#327861}