No spawn on manual remove of parentless RH and/or SX tasks

[dwsutherland]

supersedes #7134

This change makes the default spawning behavior on manual (command) remove of parentless runahead (RH) and sequential xtriggered (SX) tasks.. They no longer spawn their next instance.

Users can always use cylc set --pre=all . . . to reintroduce the tasks.
And of course, not remove but, set (xtrig or outputs) or skip to spawn forward otherwise

This removes the need to reinstate the --no-spawn option in #7134

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.