[Scott-Owen-James]

closes #7175

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[Scott-Owen-James]

Note to self for when you return from holiday:

• Sort out obsoletion message.
• Make sure it's in the right place as a config.

[Scott-Owen-James]

Adding an obsoletion message for suicide triggers in the same manner of other obsoletions in the workflow file is proving to be a shade complicated due to it's format, it doesn't appear to identify the existence of a suicide trigger when it passes it to the upgrader, might be easier to leave the current message method and modify it to announce obsoletion instead.

[oliver-sanders]

@Scott-Owen-James, the goal was to remove the experimental config and add a u.obsolete line so that continuing to configure it gives a warning.