Revert of Add d8 target to the GN build.

Revert of Add d8 target to the GN build. (patchset #2 id:40001 of https://codereview.chromium.org/834113005/)

Reason for revert:
V8 roll fails due to this change. (see https://codereview.chromium.org/843673003/)

Original issue's description:
> Add d8 target to the GN build.
>
> Also formats the rest of the file with "gn format". This accounts for all the changes except for the "d8" target additions.
>
> Committed: https://crrev.com/36383f08c1f692ea797d54a27d7c6b3d3d53b440
> Cr-Commit-Position: refs/heads/master@{#25984}

TBR=jochen@chromium.org,machenbach@chromium.org,brettw@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/ef50fdfdb05e1a3a3822962f5235b804218a5f4e
Cr-Commit-Position: refs/heads/master@{#25985}

[Yang, 2015-01-08 08:37:15]

Created Revert of Add d8 target to the GN build.

[commit-bot: I haz the power, 2015-01-08 08:38:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/838983002/1

[commit-bot: I haz the power, 2015-01-08 08:38:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-08 08:38:34]

Patchset 1 (id:??) landed as
https://crrev.com/ef50fdfdb05e1a3a3822962f5235b804218a5f4e
Cr-Commit-Position: refs/heads/master@{#25985}

[Yang, 2015-01-08 13:21:03]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/833563004/ by yangguo@chromium.org.

The reason for reverting is: Relanding because this is not actually blocking the
roll..