Reclassify OFL as notice per cl/537072410

# *** THIS PACKAGE HAS SPECIAL LICENSING CONDITIONS.  PLEASE

#     CONSULT THE OWNERS AND opensource-licensing@google.com BEFORE

#     DEPENDING ON IT IN YOUR PROJECT. ***

third_party {

  license_note: "would be NOTICE save for OFL in:\n"

  "   fonts/README\n"

  "   fonts/OFL.txt\n"

  license_type: BY_EXCEPTION_ONLY

  license_type: NOTICE

}