Drop VIRTUAL_ENV

The environment is automatically set by tox.

Also remove the requirements target because it is not actually used in
CI and is quite commonly maintained in individual repos.

Change-Id: I8f4025ebe8d373a53bd42eeb5b23c6576b40bcab

tox.ini

@@ -5,8 +5,8 @@ ignore_basepython_conflict = True
 
 [testenv]
 usedevelop = True
-setenv = VIRTUAL_ENV={envdir}
-         PYTHONWARNINGS=always::DeprecationWarning
+setenv =
+  PYTHONWARNINGS=always::DeprecationWarning
 install_command =
     pip install {opts} {packages}
 allowlist_externals = find
@@ -204,13 +204,6 @@ commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
-[testenv:requirements]
-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'
-
 [testenv:pip-missing-reqs]
 deps = pip-check-reqs>=2.3.2
        -r{toxinidir}/requirements.txt