tests/test-backwards-remove.t

cleanupnode: do not use generator for node mapping

The 'successors' part of the mappings used of be a tuple. This avoid issue from
code consuming the generator "by mistake". For example, an extension inspecting the
mapping content used to be able to iterate over the successors mapping without
consequence.

Since the mapping are small we do not expect any performance impact we use tuple
again for this.

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ ls
  a
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

B should disappear

  $ ls
  a