Remove GYP files.

sandbox/sandbox.gyp

-# Copyright (c) 2012 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.
-
-{
-  'variables': {
-    'chromium_code': 1,
-  },
-  'conditions': [
-    [ 'OS=="win"', {
-      'includes': [
-        'win/sandbox_win.gypi',
-      ],
-    }],
-    [ 'OS=="linux" or OS=="android"', {
-      'includes': [
-        'linux/sandbox_linux.gypi',
-      ],
-    }],
-    [ 'OS=="mac" and OS!="ios"', {
-      'includes': [
-        'mac/sandbox_mac.gypi',
-      ],
-    }],
-    [ 'OS!="win" and OS!="mac" and OS!="linux" and OS!="android"', {
-      # A 'default' to accomodate the "sandbox" target.
-      'targets': [
-        {
-          'target_name': 'sandbox',
-          'type': 'none',
-        }
-       ]
-    }],
-  ],
-}