Remove deprecated `types` in `.gitlab-ci.yml`

We are still supporting the deprecated keyword types in our pipeline configuration file, that has been replaced with stages: https://docs.gitlab.com/ee/ci/yaml/README.html#types.

We should consider the impact of removing the support for it, in order to keep the codebase cleaner.

Pros

• we remove one deprecated item from our product
• codebase will be cleaner

Cons

• pipelines with very old configuration still using types will stop working
• it is not easy to spot if some of your projects is using this keyword without inspecting each possible case
• a project may have multiple configuration files (different branches), or pipelines scheduled for old commits

Questions

1. can we get some data about how many pipelines that are actually running on GitLab.com still rely on this keyword?
2. can we add a warning message in the project if we detect this?