Remove HarfBuzzFaceCoreText

Since the rest of the OS X drawing code moved to FontHarfBuzz
and mostly the Skia based code, we can remove the special cased
metrics callback implementation here.

BUG=419386
R=eae, behdad

Review URL: https://codereview.chromium.org/619923003

git-svn-id: svn://svn.chromium.org/blink/trunk@183157 bbb929c8-8fbe-4397-9dbb-9b2b20218538