Clean up Mojo C API dependent targets

ui/platform_window/mojo/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("//mojo/public/tools/bindings/mojom.gni")
 
 # This target does NOT depend on skia. One can depend on this target to avoid
 # picking up a dependency on skia.
 component("mojo") {
   output_name = "mojo_ime_lib"
 
   public_deps = [
     "//ui/base/ime",
   ]
   deps = [
     ":interfaces",
     "//base",
-    "//mojo/public/c/system:for_component",
     "//ui/platform_window",
   ]
 
   defines = [ "MOJO_IME_IMPLEMENTATION" ]
 
   sources = [
     "ime_type_converters.cc",
     "ime_type_converters.h",
     "mojo_ime_export.h",
   ]
 }
 
 mojom("interfaces") {
   sources = [
     "text_input_state.mojom",
   ]
 }