Remove local-oldest-requirements files (#8863)

This is part of https://github.com/certbot/certbot/issues/8787. I got a +1 from our packagers at major distros in https://github.com/certbot/certbot/issues/8761.

* remove local-oldest-requirements files

* fix tests

* fix some oldest tests

* list packages on one line in tox.ini

* add changelog entry

.azure-pipelines/templates/steps/sphinx-steps.yml

@@ -2,14 +2,12 @@ steps:
   - bash: |
       FINAL_STATUS=0
       declare -a FAILED_BUILDS
-      python3 -m venv .venv
-      source .venv/bin/activate
-      python tools/pipstrap.py
+      tools/venv.py
+      source venv/bin/activate
       for doc_path in */docs
       do
         echo ""
         echo "##[group]Building $doc_path"
-        tools/pip_install_editable.py $doc_path/..[docs]
         if ! sphinx-build -W --keep-going -b html $doc_path $doc_path/_build/html; then
           FINAL_STATUS=1
           FAILED_BUILDS[${#FAILED_BUILDS[@]}]="${doc_path%/docs}"