26.8.0-trunk.155.0611.205643

runners: make remove work via --api with named params and a range

remove was an internal positional helper (remove <name> <index>) and
ignored the named gh_token/runner_name/start/stop params, so an --api
call like `remove runner_name=ampere-1 start=76 stop=80` operated on a
literal runner named "runner_name=ampere-1" and removed nothing.

Worse, prefix/registration_url were derived only inside the install
branch, so remove/remove_online/purge built a malformed
'//actions/runners' URL that matched no runners.

- Derive prefix/registration_url before the case so every subcommand
  reaches the GitHub API.
- remove now accepts both the internal positional form and an --api
  named call with a start..stop range, removing <name>-<index> on GitHub
  and the matching actions-runner-<index> locally; returns non-zero if
  any GitHub delete failed (preserves install's skip-if-busy behavior).
- purge: pass the index to remove (was dropping it).