Update `project.yaml` examples to pipeline v4 if the example only has ehrQL actions

[alarthast]

• Part of upgrading pipeline to version 4
• Version 4 of pipeline removes support for cohort extractor and the project.yaml file should not have an expectations section.
• case-control-studies.md has examples that use cohort extractor actions so nothing has been changed there. Is there a reason why this page wasn't updated to use ehrQL?