Fix several type annotations for mypy 0.4.6 compatibility.

A few functions had arguments removed without having their type
annotations updated accordingly. As a result mypy version 0.4.6
thinks that the first type in the annotation is supposed to be
the type of `self`, a new mypy feature which we are not intending
to use here.

zerver/lib/test_helpers.py

@@ -189,7 +189,7 @@ def get_user_messages(user_profile):
 
 class DummyHandler(object):
     def __init__(self):
-        # type: (Callable) -> None
+        # type: () -> None
         allocate_handler_id(self)  # type: ignore # this is a testing mock
 
 class POSTRequestMock(object):