Revert of [mb] Switch staging bot to gyp for testing purposes

infra/mb/mb_config.pyl

 # Copyright 2016 The V8 project 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 a map of buildbot master names -> buildbot builder names ->
   # config names (where each config name is a key in the 'configs' dict,
   # below). MB uses this dict to look up which config to use for a given bot.
   'masters': {
     'client.v8': {
-      'V8 Linux - swarming staging': 'gyp_swarming_release',
+      'V8 Linux - swarming staging': 'gn_swarming_release',
     },
   },
 
   'configs': {
     'gyp_swarming_release': [
       'release_bot', 'swarming_bot', 'gyp'],
     'gn_swarming_release': [
       'release_bot', 'swarming_bot', 'gn'],
   },
 
@@ skipping 48 matching lines @@
     'swarming': {
       'gn_args': 'v8_test_isolation_mode="prepare"',
       'gyp_defines': 'test_isolation_mode=prepare',
     },
 
     'swarming_bot': {
       'mixins': ['swarming', 'no_sysroot', 'no_icu_data_file'],
     },
   },
 }