Remove python 2.5 compatibility code.

rietveld.py

 # 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.
 """Defines class Rietveld to easily access a rietveld instance.
 
 Security implications:
 
 The following hypothesis are made:
 - Rietveld enforces:
   - Nobody else than issue owner can upload a patch set
   - Verifies the issue owner credentials when creating new issues
   - A issue owner can't change once the issue is created
   - A patch set cannot be modified
 """
 
+import json
 import logging
-import os
 import re
-import sys
 import time
 import urllib2
 
-try:
-  import simplejson as json  # pylint: disable=F0401
-except ImportError:
-  try:
-    import json  # pylint: disable=F0401
-  except ImportError:
-    # Import the one included in depot_tools.
-    sys.path.append(os.path.join(os.path.dirname(__file__), 'third_party'))
-    import simplejson as json  # pylint: disable=F0401
-
 from third_party import upload
 import patch
 
 # Hack out upload logging.info()
 upload.logging = logging.getLogger('upload')
 # Mac pylint choke on this line.
 upload.logging.setLevel(logging.WARNING)  # pylint: disable=E1103
 
 
 class Rietveld(object):
@@ skipping 300 matching lines @@
           if not 'Name or service not known' in e.reason:
             # Usually internal GAE flakiness.
             raise
         # If reaching this line, loop again. Uses a small backoff.
         time.sleep(1+maxtries*2)
     finally:
       upload.ErrorExit = old_error_exit
 
   # DEPRECATED.
   Send = get