Fix #476: Revert "Try import django.utils.simplejson, except import json"

This reverts commit 4e6db78952.

compressor/cache.py

@@ -1,3 +1,4 @@
+import json
 import hashlib
 import os
 import socket
@@ -9,11 +10,6 @@ from django.utils.encoding import force_text, smart_bytes
 from django.utils.functional import SimpleLazyObject
 from django.utils.importlib import import_module
 
-try:
-    import django.utils.simplejson as json
-except ImportError:
-    import json
-
 from compressor.conf import settings
 from compressor.storage import default_storage
 from compressor.utils import get_mod_func