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: I53ae237d0da4195f974ac3fac3ffe0b713d773ce

tox.ini

@@ -14,7 +14,6 @@ passenv =
 
 basepython = python3
 #usedevelop = True
-setenv = VIRTUAL_ENV={envdir}
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
@@ -30,7 +29,6 @@ commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:fast-specs]
 description = Build only specs that have changed since last commit
-envdir = {toxworkdir}/docs
 commands = bash tools/fast-specs.sh
 
 [testenv:pep8]
@@ -51,13 +49,11 @@ exclude = .venv,.git,.tox,doc,.eggs
 # fails if we don't have it.
 deps = launchpadlib
        simplejson
-envdir={toxworkdir}/launchpadlib
 commands =
   python {toxinidir}/tools/move_implemented_specs.py {posargs}
 
 [testenv:count-blueprints]
 deps = {[testenv:move-implemented-specs]deps}
-envdir={toxworkdir}/launchpadlib
 commands =
   python {toxinidir}/tools/count_blueprints.py {posargs}
 
@@ -65,7 +61,6 @@ commands =
 # Usage:
 # tox -e move-spec -- [--dry-run] [--verbose] path/to/spec.rst path/to/destdir
 deps=
-envdir={toxworkdir}/nodeps
 commands =
   python {toxinidir}/tools/move_spec.py {posargs}
 
@@ -73,6 +68,5 @@ commands =
 # Usage:
 # tox -e abandon-spec -- [--dry-run] [--verbose] path/to/obsolete-spec.rst
 deps=
-envdir={toxworkdir}/nodeps
 commands =
   python {toxinidir}/tools/abandon_spec.py {posargs}