Remove obsolete Mac specific code from SimpleFontData

Remove a bunch of Mac specific code from SimpleFontData that is no
longer used since the switch to HarfBuzz.

BUG=286450
R=dominik.rottsches@intel.com

Review URL: https://codereview.chromium.org/621983004

git-svn-id: svn://svn.chromium.org/blink/trunk@183138 bbb929c8-8fbe-4397-9dbb-9b2b20218538