tox: Drop envdir

tox now always recreates an env although the env is shared using envdir
options.
~~~
$ tox -e genpolicy
genpolicy: recreate env because env type changed from
{'name': 'genconfig', 'type': 'VirtualEnvRunner'} to
{'name': 'genpolicy', 'type': 'VirtualEnvRunner'}
~~~

According to the maintainer of tox, this functionality is not intended
to be supported.
https://github.com/tox-dev/tox/issues/425#issuecomment-1011944293

Change-Id: If340525da5b27bd9704f113a76d1fa992790ab9e
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

tox.ini

@@ -10,7 +10,6 @@ allowlist_externals =
     rm
 install_command = pip install {opts} {packages}
 setenv =
-   VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
 deps =
     -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
@@ -102,7 +101,6 @@ import-order-style = pep8
 enable-extensions=H106,H203,H204,H205,H904
 
 [testenv:bashate]
-envdir = {toxworkdir}/shared
 commands = bash -c "find {toxinidir}             \
          -not \( -type d -name .tox\* -prune \)  \
          -not \( -type d -name .venv\* -prune \) \
@@ -133,7 +131,7 @@ deps =
   -egit+https://opendev.org/openstack/requirements#egg=openstack-requirements
 allowlist_externals = sh
 commands =
-    sh -c '{envdir}/src/openstack-requirements/playbooks/files/project-requirements-change.py --req {envdir}/src/openstack-requirements --local {toxinidir} master'
+  sh -c '{envdir}/src/openstack-requirements/playbooks/files/project-requirements-change.py --req {envdir}/src/openstack-requirements --local {toxinidir} master'
 
 [testenv:bandit]
 commands = bandit -r octaviaclient -ll -ii -x tests