Cleanup TreeShared and Node

This patch removes the following deadcode from TreeShared and Node:
  Node::renderRect
  Node::pixelSnappedRenderRect
  Node::textRects
  TreeShared::hasOneRef

Review URL: https://codereview.chromium.org/100113006

git-svn-id: svn://svn.chromium.org/blink/trunk@163923 bbb929c8-8fbe-4397-9dbb-9b2b20218538