This patch makes a number of related improvements:

* Displays relevant bindings in innermost-first order.
  The inner ones are closer to the error.

* Does not display syntactically top-level bindings,
  unless you say -fno-max-relevant-bindings.
  This is what Trac #8233 was mainly about

* Makes the TopLevelFlag in a TcIdBinder really mean
  "syntactically top level".  It was a bit vague before.

There was some associated simplification, because we no longer
need to pas a TopLevelFlag to tcMonoBinds and friends.