Drop redundant injection of VIRTUAL_ENV

tox automatically injects the environment so no manual override is
necessary.

Also remove basepython because tox uses the python version where tox
is installed by default, and we no longer expect that the tests may run
in env with python 2.

Change-Id: I4082aedf525f8d39dc65236d74e4063d3ae3a1ba

tox.ini

@@ -1,17 +1,15 @@
 [tox]
 envlist = pypy,py39,pep8
-ignore_basepython_conflict = true
 minversion = 3.18.0
 
 [testenv]
-basepython = python3
-setenv = VIRTUAL_ENV={envdir}
 usedevelop = True
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
-commands = find . -type f -name "*.py[c|o]" -delete
+commands =
+  find . -type f -name "*.py[c|o]" -delete
   stestr run --slowest {posargs}
 allowlist_externals = find