Fix requirements

requirements.txt

 git+https://git.autistici.org/ai/sso.git@nonce#egg=sso&subdirectory=src/python
 Flask
-backoff
-requests

setup.py

@@ -11,8 +11,6 @@ setup(
     author_email="info@autistici.org",
     url="https://git.autistici.org/ai3/python-mailman-api",
     install_requires=["Flask",
-                      "backoff",
-                      "requests",
                       "sso"],
     packages=find_packages(),
     entry_points={