Remove unused FontData::containsCharacters().

The function was used by WebKit WX port.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/163613005

git-svn-id: svn://svn.chromium.org/blink/trunk@167148 bbb929c8-8fbe-4397-9dbb-9b2b20218538