New Mojom parser: Remove dependency on CGO.

mojom/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 group("mojom") {
   testonly = true
-  deps = [
-    ":tests",
-  ]
+  deps = []
   if (is_linux && defined(go_build_tool) && go_build_tool != "") {
     deps += [ "//mojom/mojom_parser" ]
   }
 }
-
-group("tests") {
-  testonly = true
-  deps = []
-  if (is_linux && defined(go_build_tool) && go_build_tool != "") {
-    deps += [ "//mojom/mojom_parser:serialization_test" ]
-  }
-}