Revert of add gn_all, gyp_all targets to build files, remove GN's //:root

Revert of add gn_all, gyp_all targets to build files, remove GN's //:root (patchset #18 id:350001 of https://codereview.chromium.org/936193004/)

Reason for revert:
Suspecting this breaks Mac builds.
http://build.chromium.org/p/chromium/builders/Mac/builds/33993

Original issue's description:
> add gn_all, gyp_all targets to the build files, remove GN's //:root
>
> In order to be able to make sure we are building the same list of targets
> in both the GYP and GN builds, this patch adds new 'gn_all' and 'gyp_all'
> targets.
>
> Eventually, we should make sure that if one builds 'gn_all', then building
> 'gyp_all', 'All', or 'all' then has nothing to do. We're not there yet, but this
> is a start.
>
> The 'gn_all' target replaces the //:root target in the GN builds.
>
> R=brettw@chromium.org
> BUG=461019
> CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:android_chromium_gn_compile_dbg,android_chromium_gn_compile_rel;tryserver.chromium.win:win8_chromium_gn_rel,win8_chromium_gn_dbg;tryserver.chromium.mac:mac_chromium_gn_rel,mac_chromium_gn_dbg
>
> Committed: https://crrev.com/ff30e3de333305ccdaa103aa7f9e46765da83e99
> Cr-Commit-Position: refs/heads/master@{#317760}

TBR=brettw@chromium.org,dpranke@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=461019
Committed: https://crrev.com/e6d374cf7ead69b3ff110f9d7dfba0dee921e6b7
Cr-Commit-Position: refs/heads/master@{#317763}

[hiroshige, 2015-02-24 07:41:03]

Created Revert of add gn_all, gyp_all targets to build files, remove GN's
//:root

[hiroshige, 2015-02-24 07:52:58]

The CQ bit was checked by hiroshige@chromium.org

[commit-bot: I haz the power, 2015-02-24 07:53:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/944573003/1

[commit-bot: I haz the power, 2015-02-24 07:54:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-24 07:54:41]

Patchset 1 (id:??) landed as
https://crrev.com/e6d374cf7ead69b3ff110f9d7dfba0dee921e6b7
Cr-Commit-Position: refs/heads/master@{#317763}

[Dirk Pranke, 2015-02-24 15:45:31]

On 2015/02/24 07:54:41, I haz the power (commit-bot) wrote:
> Patchset 1 (id:??) landed as
> https://crrev.com/e6d374cf7ead69b3ff110f9d7dfba0dee921e6b7
> Cr-Commit-Position: refs/heads/master@{#317763}

lgtm, thanks for taking care of this!