Remove GN GYP generator.

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
 # In GN, a "group" is a dummy target that just lists other targets.
 group("root") {
-  # Declares that this target should be treated as "external" in the GN-GYP
-  # hybrid build, and GN will not generate a GYP file for it. This flag is
-  # ignored in the pure GN build.
-  external = true
-
   # Note that some dependencies are commented out. These are things that are
   # currently written but not hooked up to the build yet. They may need to be
   # completed or possibly just tested and then re-enabled.
   deps = [
     # This is a temporary test of the not-yet-complete NaCl cross-compilation.
     #"//base(//build/toolchain/nacl:x86_newlib)",
 
     #"//chrome",
     #"//components/language_usage_metrics",
     #"//components/navigation_metrics",
@@ skipping 10 matching lines @@
     #"//third_party/WebKit/Source/platform",
     #"//third_party/icu:icudata",
     #"//third_party/leveldatabase",
     #"//third_party/libpng",
     #"//third_party/zlib",
     #"//skia",
     "//tools/gn",
     #"//url",
   ]
 }