nghttpd: Use util::utos instead of slow util::to_str

src/HttpServer.cc

@@ -613,7 +613,7 @@ int Http2Handler::submit_file_response(const std::string& status,
                                        nghttp2_data_provider *data_prd)
 {
   std::string date_str = util::http_date(time(0));
-  std::string content_length = util::to_str(file_length);
+  std::string content_length = util::utos(file_length);
   std::string last_modified_str;
   auto nva = std::vector<nghttp2_nv>{
     http2::make_nv_ls(":status", status),

src/util.h

@@ -212,14 +212,6 @@ std::string http_date(time_t t);
 
 time_t parse_http_date(const std::string& s);
 
-template<typename T>
-std::string to_str(T value)
-{
-  std::stringstream ss;
-  ss << value;
-  return ss.str();
-}
-
 template<typename InputIterator1, typename InputIterator2>
 bool startsWith
 (InputIterator1 first1,