tests/test-empty-dir.t

branchmap: remove the droppednodes logic

It was unused. note how it is only extended if the list is empty. So it's always
empty at the end.

We could try to fix that, however this would part of the code is to be removed
in the next changeset as we do not run `branchmap` on truncated repo since
`repoview` in 2.5.

  $ hg init

  $ echo 123 > a
  $ hg add a
  $ hg commit -m "first" a

  $ mkdir sub
  $ echo 321 > sub/b
  $ hg add sub/b
  $ hg commit -m "second" sub/b

  $ cat sub/b
  321

  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cat sub/b 2>/dev/null || echo "sub/b not present"
  sub/b not present

  $ test -d sub || echo "sub not present"
  sub not present