Remove deprecated APIs

include/fmt/format-inl.h

@@ -2341,12 +2341,6 @@ FMT_FUNC void report_system_error(int error_code,
   report_error(format_system_error, error_code, message);
 }
 
-// DEPRECATED!
-// This function is defined here and not inline for ABI compatiblity.
-FMT_FUNC void detail::error_handler::on_error(const char* message) {
-  throw_format_error(message);
-}
-
 FMT_FUNC std::string vformat(string_view fmt, format_args args) {
   // Don't optimize the "{}" case to keep the binary size small and because it
   // can be better optimized in fmt::format anyway.