fix(skeleton): remove useless gitlab-ci.yaml since actual file is gitlab-ci.yml

--HG--
branch : 3.28

cubicweb/skeleton/.gitlab-ci.yaml.tmpl

-image: python
-
-stages:
-  - tests
-  - after-tests
-
-before_script:
-  - pip install tox
-
-py3:
-  stage: tests
-  script: tox -e py3
-
-flake8:
-  stage: tests
-  script: tox -e flake8
-
-check-manifest:
-  stage: tests
-  script: tox -e check-manifest
-
-black:
-  stage: tests
-  script: tox -e black
-
-# If you have mypy set up
-# mypy:
-#   stage: tests
-#   script: tox -e mypy
-
-# If you have your project on readthedocs, you can automatically trigger its
-# build by setting:
-# - READTHEDOCS_TOKEN
-# - READTHEDOCS_ID
-# in your heptapod project Settings > CI/CD > Variables.
-# You can find those secrets by creating a new integration in your readthedocs
-# project here: https://readthedocs.org/dashboard/cubicweb_%(cubename)s/integrations/
-#
-# Related documentation:
-# https://docs.readthedocs.io/en/latest/webhooks.html#using-the-generic-api-integration
-#
-# trigger-readthedocs:
-#   only:
-#     refs:
-#       - branch/default
-#   stage: after-tests
-#   script:
-#   # regarding the " everywhere when there is a '%%': yaml is extremly weird when %% are involved
-#   - curl -X POST -d "token=${READTHEDOCS_TOKEN}" https://readthedocs.org/api/v2/webhook/cubicweb_%(cubename)s/${READTHEDOCS_ID} -w "\nhttp code:"\ "%%{http_code}\n" -f