Drop WriteTimeout on the default http.Server

It was acting as an upper limit for the request lifetime, which isn't
necessary on internal services.

serverutil/http.go

@@ -73,8 +73,7 @@ func (config *ServerConfig) buildHTTPServer(h http.Handler) (*http.Server, error
 	// reconnections low.
 	return &http.Server{
 		Handler:           addDefaultHandlers(h),
-		ReadTimeout:  30 * time.Second,
-		WriteTimeout: 30 * time.Second,
+		ReadHeaderTimeout: 30 * time.Second,
 		IdleTimeout:       600 * time.Second,
 		TLSConfig:         tlsConfig,
 	}, nil