Revert "Try to retry InvalidRequestError from sqlalchemy"

This reverts commit 4d0223e305.

well, that didn't work

tailbone/tweens.py

@@ -27,7 +27,7 @@ Tween Factories
 from __future__ import unicode_literals, absolute_import
 
 import six
-from sqlalchemy.exc import OperationalError, InvalidRequestError
+from sqlalchemy.exc import OperationalError
 
 
 def sqlerror_tween_factory(handler, registry):
@@ -56,7 +56,7 @@ def sqlerror_tween_factory(handler, registry):
 
         try:
             response = handler(request)
-        except (OperationalError, InvalidRequestError) as error:
+        except OperationalError as error:
 
             # if connection is invalid, allow retry
             if error.connection_invalidated: