Remove out of date comment from Font.cpp

Remove an out of data comment that no longer applies.

TBR=dominik.rottsches@intel.com
NOTRY=true

Review URL: https://codereview.chromium.org/640793002

git-svn-id: svn://svn.chromium.org/blink/trunk@183421 bbb929c8-8fbe-4397-9dbb-9b2b20218538