Remove the _cpp_sources target from mojom.

services/service_manager/public/cpp/BUILD.gn

 # Copyright 2014 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.
 
 group("cpp") {
   public_deps = [
     ":sources",
   ]
 }
 
@@ skipping 69 matching lines @@
       ":cpp",
       "//testing/gtest",
     ]
 
     deps = [
       "//base",
       "//base/test:test_support",
       "//mojo/public/cpp/bindings",
       "//mojo/public/cpp/system",
       "//services/service_manager/background:lib",
-      "//services/service_manager/public/interfaces:interfaces_cpp_sources",
+      "//services/service_manager/public/interfaces",
     ]
 
     data_deps = []
   }
 }