Removes assert of message confirming to protocol.

Two reasons for removal:
- On the path of removing most non-postconditional asserts.
  Since the asserts on every message is incurring a
  non-insignificant penalty on large datasets.
- Since the assert was invoked as a function, the 'right side'
  of the assert statement, i.e. the error message was being invoked
  as a function, discovered since the __repr__ of the message was
  high on the bottleneck list.

zipline/gens/sort.py

@@ -20,7 +20,6 @@ import logbook
 
 from collections import deque
 from zipline.gens.utils import (
-    assert_datasource_unframe_protocol,
     assert_sort_protocol
 )
 
@@ -44,10 +43,6 @@ def date_sort(stream_in, source_ids):
 
     # Process incoming streams.
     for message in stream_in:
-        # Incoming messages should be the output of DATASOURCE_UNFRAME.
-        assert_datasource_unframe_protocol(message), \
-            "Bad message in date_sort: %s" % message
-
         # Only allow messages from sources we expect.
         assert message.source_id in sources, "Unexpected source: %s" % message