Remove unused string left over from a prior MB unittest.

tools/mb/mb_unittest.py

 #!/usr/bin/python
 # 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.
 
 """Tests for mb.py."""
 
 import json
 import StringIO
 import os
@@ skipping 161 matching lines @@
     },
     'rel': {
       'gn_args': 'is_debug=false',
     },
   },
   'private_configs': ['private'],
   'unsupported_configs': ['unsupported'],
 }
 """
 
-
-TEST_BAD_CONFIG_ERR = """\
-mb config file /fake_src/tools/mb/mb_config.pyl has problems:
-  Config "gn_rel_bot_1" used by a bot is also listed in "common_dev_configs".
-  Unknown config "unsupported" referenced from "unsupported_configs".
-  Unknown config "private" referenced from "private_configs".
-  Public artifact builder "a" can not contain the "chrome_with_codecs" mixin.
-  Public artifact builder "b" can not contain the "chrome_with_codecs" mixin."""
-
-
 class UnitTest(unittest.TestCase):
   def fake_mbw(self, files=None, win32=False):
     mbw = FakeMBW(win32=win32)
     mbw.files.setdefault(mbw.default_config, TEST_CONFIG)
     if files:
       for path, contents in files.items():
         mbw.files[path] = contents
     return mbw
 
   def check(self, args, mbw=None, files=None, out=None, err=None, ret=None):
@@ skipping 243 matching lines @@
     self.check(['validate'], mbw=mbw, ret=0)
 
   def test_bad_validate(self):
     mbw = self.fake_mbw()
     mbw.files[mbw.default_config] = TEST_BAD_CONFIG
     self.check(['validate'], mbw=mbw, ret=1)
 
 
 if __name__ == '__main__':
   unittest.main()