Change 'nonleaf' rank name

Since there would no longer be a leaf name, having a nonleaf name doesn't make sense.

If we have the name 'nosafepoint' and the name 'safepoint' we can infer safepoint_check_always and safepoint_check_never so we can remove this parameter and test using the rank value.

Or max_safepoint as the rank name?

or maxrank which is shorter? or top or max?

  enum class Rank {
       event,
       service = event + 6,
       stackwatermark = service + 3,
       tty = stackwatermark + 3,
       oopstorage = tty + 3,
       nosafepoint = oopstorage + 6,
       safepoint = nosafepoint + 20
  };