Remove unnecessary mypy config

Only one value is still relevant, and it is already specified in
pyproject.toml.

Author: WhyNotHugo

tox.ini

@@ -35,9 +35,3 @@ deps = vermin
 commands =
   vermin -t=3.9- --eval-annotations --backport enum --backport importlib --backport typing --no-parse-comments --violations .
 skip_install = true
-
-[mypy]
-# Silence warnings given by using untyped libraries:
-ignore_missing_imports = True
-# See https://github.com/python/mypy/issues/7511:
-warn_no_return = False