Also provide a cleaner, better documented and slightly faster
implementation.

- block_strictly_dominates() is trivially to compute yourself anyway.
- free_dom() and free_postdom() did not free any memory anyway and the
  irg_properties handling is performed by confirm_irg_properties()
  anyway.

There are no middleend jump nodes at this point anymore.

The ILP blockscheduler couldn't create optimal schedules anyway (because
we heuristically inserted loop breakers into the ILP)

We only use control flow scc analysis.

== and != comparisons are always lowered with the "or trick" so no need
to have the other lowering code around.