Cleanup GN BUILD files, gni's and imports.

mandoline/app/desktop/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("//third_party/mojo/src/mojo/public/mojo.gni")
-
 group("desktop") {
   deps = [
     ":mandoline",
   ]
 }
 
 executable("mandoline") {
   sources = [
     "../core_services_initialization.cc",
     "launcher_process.cc",
     "launcher_process.h",
     "main.cc",
   ]
 
   deps = [
     "//base",
     "//build/config/sanitizers:deps",
     "//mojo/common",
     "//mojo/environment:chromium",
     "//mojo/runner:lib",
   ]
 
   data_deps = [
     "//components/html_viewer",
     "//mandoline/services/core_services/",
   ]
 }