Removed unused isContainedInParentBoundingBox method

This method was added in a hack to fix a link highlight issue. Now that
it's been fixed in r165024 this method is no longer needed.

BUG=

Review URL: https://codereview.chromium.org/137793009

git-svn-id: svn://svn.chromium.org/blink/trunk@165164 bbb929c8-8fbe-4397-9dbb-9b2b20218538