build: fix GN build for ngtcp2

PR-URL: https://github.com/nodejs/node/pull/56300
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
Reviewed-By: Xuguang Mei <meixuguang@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

deps/ngtcp2/unofficial.gni

@@ -68,8 +68,7 @@ template("ngtcp2_gn_build") {
       cflags_c = [
         "-Wno-extra-semi",
         "-Wno-implicit-fallthrough",
-        # Remove after https://github.com/ngtcp2/ngtcp2/issues/1050 is fixed.
-        "-Wno-sometimes-uninitialized",
+        "-Wno-unused-function",
       ]
     }
   }