[Coordinated Graphics] Remove unused method in CoordinatedGraphicsLayer

[Coordinated Graphics] Remove unused method in CoordinatedGraphicsLayer
https://bugs.webkit.org/show_bug.cgi?id=120664

Patch by Jae Hyun Park <jae.park@company100.net> on 2013-09-04
Reviewed by Darin Adler.

CoordinatedGraphicsLayer::hasPendingVisibleChanges is not used as of
r148952.

* platform/graphics/texmap/coordinated/CoordinatedGraphicsLayer.cpp:
* platform/graphics/texmap/coordinated/CoordinatedGraphicsLayer.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@155045 268f45cc-cd09-0410-ab3c-d52691b4dbfc