Remove pytest-runner

conftest.py

@@ -0,0 +1,9 @@
+import sys
+from importlib.util import find_spec
+
+
+def pytest_addoption(parser, pluginmanager):
+    # Ignore the "--mypy" argument if pytest-mypy is not installed and
+    # the implementation is not cpython
+    if sys.implementation.name != 'cpython' and not find_spec("pytest_mypy"):
+        parser.addoption("--mypy", action="store_true")