Update testenv config

Author: domdfcoding

tox.ini

@@ -243,12 +243,12 @@ setenv =
 setenv =
     PYTHONDEVMODE=1
     PIP_DISABLE_PIP_VERSION_CHECK=1
+    SETUPTOOLS_USE_DISTUTILS=stdlib
 deps =
     -r{toxinidir}/tests/requirements.txt
     click7.1: click~=7.1.0
     click7.1: types-click==7.1.8
     click8.0: click~=8.0.0
-extras = all
 commands =
     python --version
     python -m pytest --cov=consolekit -r aR tests/ {posargs}