chore: Revert "build: integrate renovate"

Description

This reverts commit f6c27ec0.

Remove the Renovate config from the repository. Grove is deprecated, and we're not reviewing these automated PRs. So these PRs are just adding noise now.

Supporting information

Private-ref: https://tasks.opencraft.com/browse/SE-6614

Testing instructions

Verify this cleanly removes all Renovate config related to this repo.

Dependencies

None

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

Other things to clean up:

• delete the pipeline schedule in https://gitlab.com/opencraft/dev/grove/-/pipeline_schedules
• delete the RENOVATE_TOKEN from the ci/cd variables.