Revert of Fix //content/plugin ax_enums gn build flake

Revert of Fix //content/plugin ax_enums gn build flake (patchset #1 id:1 of https://codereview.chromium.org/1343883003/ )

Reason for revert:
This broke Win x64 GN builds:

ERROR Dependency cycle:
  //content:content ->
  //content/public/plugin:plugin_sources ->
  //content/plugin:plugin ->
  //content/public/common:common ->
  //content:content

Original issue's description:
> Fix //content/plugin ax_enums gn build flake
>
> Flake observerd with target_os="android" and enable_plugins=true:
> //content/plugin/plugin_thread.cc ends up including the generated
> ax_enums header so make it depend on it.
>
> BUG=
>
> Committed: https://crrev.com/d050925ac8f0324186269b1f10c0a8a9d24fab40
> Cr-Commit-Position: refs/heads/master@{#348918}

TBR=ananta@chromium.org,jam@chromium.org,tsniatowski@opera.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/e30f93f245b69706b6155326a3d78a8999129039
Cr-Commit-Position: refs/heads/master@{#348927}

[Devlin, 2015-09-15 17:48:03]

Created Revert of Fix //content/plugin ax_enums gn build flake

[commit-bot: I haz the power, 2015-09-15 17:49:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1339173003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1339173003/1

[commit-bot: I haz the power, 2015-09-15 17:51:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-15 17:52:25]

Patchset 1 (id:??) landed as
https://crrev.com/e30f93f245b69706b6155326a3d78a8999129039
Cr-Commit-Position: refs/heads/master@{#348927}

[commit-bot: I haz the power, 2015-09-23 12:46:39]

Patchset 1 (id:??) landed as
https://crrev.com/e30f93f245b69706b6155326a3d78a8999129039
Cr-Commit-Position: refs/heads/master@{#348927}