Remove ChromeClient::fullScreenRendererChanged().
<https://webkit.org/b/126370>

This hook was added in r75277 to notify WebFullScreenController when
the full screen renderer changed. In r110216 the code was refactored,
making this notification unnecessary.

Reviewed by Antti Koivisto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161203 268f45cc-cd09-0410-ab3c-d52691b4dbfc