tox: Remove basepython

This follows a similar change in Kayobe [1].

[1] https://review.opendev.org/c/openstack/kayobe/+/947726

Change-Id: I661694cf9a49fd471fc83e0b5b1c0eedc3ab7767

Author: priteau

tox.ini

@@ -10,6 +10,5 @@ deps =
     -r{toxinidir}/test-requirements.txt
 
 [testenv:pep8]
-basepython = python3
 commands =
   yamllint etc/kayobe