NaCl/GYP: remove references to prep_toolchain.

third_party/jsoncpp/jsoncpp_nacl.gyp

 # 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.
 
 {
   'includes': [
     '../../build/common_untrusted.gypi',
     'jsoncpp.gypi',
   ],
   'conditions': [
     ['disable_nacl==0 and disable_nacl_untrusted==0', {
       'targets': [
         {
           'target_name': 'jsoncpp_nacl',
           'type': 'none',
           'variables': {
             'nacl_untrusted_build': 1,
             'nlib_target': 'libjsoncpp_nacl.a',
             'build_newlib': 1,
           },
           'gcc_compile_flags': [
             # Turn off optimizations based on strict aliasing
             # because of the workaround at
             # overrides/src/lib_json/json_value.cpp:38.
             '-fno-strict-aliasing',
           ],
-          'dependencies': [
-            '<(DEPTH)/native_client/tools.gyp:prep_toolchain',
-          ],
         },
       ],
     }],
   ],
 }