Fix unbound-control stdin commands for multi-process Unbounds (#1069)

Fix unbound-control stdin commands for multi-process Unbounds (#1069)

- Fix unbound-control commands that read stdin in multi-process
  operation (local_zones_remove, local_zones, local_datas_remove,
  local_datas, view_local_datas_remove, view_local_datas). They will
  be properly distributed to all processes. dump_cache and load_cache
  are no longer supported in multi-process operation.

 - Remove testdata/remote-threaded.tdir. testdata/09-unbound-control.tdir
  now checks both single and multi process/thread operation.

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Co-authored-by: Wouter Wijngaards <wcawijngaards@users.noreply.github.com>