[chromium] Remove unused transitional #defines from Platform API
https://bugs.webkit.org/show_bug.cgi?id=105971

Patch by James Robinson <jamesr@chromium.org> on 2013-01-02
Reviewed by Adrienne Walker.

These are leftovers from multi-sided patches that landed months ago.

* chromium/public/WebContentLayerClient.h:
(WebContentLayerClient):
* chromium/public/WebLayer.h:
* chromium/public/WebLayerTreeView.h:
* chromium/public/WebThread.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138687 268f45cc-cd09-0410-ab3c-d52691b4dbfc