[JENKINS-24380] Stop relying on the format of Run.id

To be merged if and when https://github.com/jenkinsci/jenkins/pull/1379 is.

Passes tests, though it is hard for me to tell if they are comprehensive enough. Discards the logic to compare timezones between publisher and receiver, which was probably a bad idea anyway; `Run.id` is intended to be a permanent unique identifier which can be referenced from various places.

Also discards numeric symlink creation. These do not exist in core after my change; in older cores, they are optional.