Drop fallback to ordereddict module

The collections module is available in Python 3.

Change-Id: I32e0b102ec4a1f2cd5c74e0ff3ed0b1e51301ba3

wsme/rest/protocol.py

@@ -1,7 +1,7 @@
+from collections import OrderedDict
 import os.path
 import logging
 
-from wsme.utils import OrderedDict
 from wsme.protocol import CallContext, Protocol, media_type_accept
 
 import wsme.rest

wsme/utils.py

@@ -111,9 +111,3 @@ def is_valid_code(code_value):
 def is_client_error(code):
     """ Checks client error code (RFC 2616)."""
     return 400 <= code < 500
-
-
-try:
-    from collections import OrderedDict
-except ImportError:
-    from ordereddict import OrderedDict  # noqa