make $info param to job_scheduler_rebuild_scheduler() required

job_scheduler_rebuild_scheduler() is only called in one place. The $info param is passed in.

So there's no need at all for this:

function job_scheduler_rebuild_scheduler($name, $info = NULL) {
  $info = $info ? $info : job_scheduler_info($name);

It's only one line of code, but the calls to job_scheduler_info() everywhere make it really hard to understand the flow of the code. This will simplify things a lot.