Remove dependency on typing package.

It’s in the standard library in Python ≥ 3.5.  (We could have used
`'typing;python_version<"3.5"'` to continue supporting earlier
versions, but we don’t.)

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

zulip/setup.py

@@ -56,7 +56,6 @@ package_info = dict(
 setuptools_info = dict(
     install_requires=['requests[security]>=0.12.1',
                       'six',
-                      'typing>=3.5.2.2',
                       'matrix_client',
                       ],
 )