Remove an unused member variable erroneously added in r149007.

* rendering/LogicalSelectionOffsetCaches.h:
(WebCore::LogicalSelectionOffsetCaches::LogicalSelectionOffsetCaches):
(LogicalSelectionOffsetCaches):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149009 268f45cc-cd09-0410-ab3c-d52691b4dbfc