tests/test-gendoc-ro.t

rebase: remove sortedstate-related confusion

The following rebase implementation details are frustrating:
- storing a list of sorted revision numbers in a field named sortedstate
- having sortedstate be a field of the rebaseruntime class
- using sortedstate[-1] as opposed to a more intuitive max(self.state) to
  compute the latest revision in the state

This commit fixes those imperfections.

#require docutils gettext

  $ $TESTDIR/check-gendoc ro
  checking for parse errors