Revert of Add chrome sync tests to the GN build.

Revert of Add chrome sync tests to the GN build. (patchset #3 id:40001 of https://codereview.chromium.org/717923006/)

Reason for revert:
This seems the most likely culprit behind sync_integration_test build and test errors that started in the patch that included this change.

Original issue's description:
> Add chrome sync tests to the GN build.
>
> This adds sync_integration_tests, sync_performance_tests, and the sync test support targets.
>
> I removed some files that were duplicated between the sync integration tests and the test support. In GYP the fact that test support was a static library hid the duplicate symbols.
>
> Add a dependency on sessions_core from sessions test support since it's required to link. Made test support target be a source set (linking source sets into static libraries will often duplicate symbols).
>
> Committed: https://crrev.com/d60468061789084ebd98458b9743726cc1541786
> Cr-Commit-Position: refs/heads/master@{#304904}

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

Committed: https://crrev.com/9d02b68215deb718ed531998323ebedd71d090bf
Cr-Commit-Position: refs/heads/master@{#305058}

[Pete Williamson, 2014-11-20 19:13:23]

Created Revert of Add chrome sync tests to the GN build.

[commit-bot: I haz the power, 2014-11-20 19:13:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/746563002/1

[commit-bot: I haz the power, 2014-11-20 19:15:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-20 19:15:48]

Patchset 1 (id:??) landed as
https://crrev.com/9d02b68215deb718ed531998323ebedd71d090bf
Cr-Commit-Position: refs/heads/master@{#305058}