chore: drop py27 testing

.gitlab-ci-extended.yml

 ---
-py27:
-  image: registry.logilab.fr/cubicweb/dockerfiles/buster-slim-pg11
-
 py3:
   image: registry.logilab.fr/cubicweb/dockerfiles/buster-slim-pg11

.gitlab-ci.yml

@@ -10,7 +10,6 @@ include:
       - "templates/lint/flake8.yml"  # will do the equivalent of 'tox -e flake8'
       - "templates/lint/check-manifest.yml"  # will do the equivalent of 'tox -e check-manifest'
       - "templates/lint/yamllint.yml"  # will do the equivalent of 'tox -e yamllint'
-      - "templates/tests/py27.yml"  # will do the equivalent of 'tox -e py27'
       - "templates/tests/py3.yml"  # will do the equivalent of 'tox -e py3'
       - "templates/create-release-on-heptapod.yml"  # this will create a release on heptapod
       - "templates/upload-to-pypi.yml"  # on a new mercurial tag (expected to be done with release-new), will push a release on pypi

tox.ini

 [tox]
-envlist = py27, py3, flake8, check-manifest, yamllint
+envlist = py3, flake8, check-manifest, yamllint
 
 [testenv]
 deps =