Stop using "zstreamdump" in tests/

zstreamdump was replaced with "zstream dump"; let's stop using the
old name, compat symlink or no.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12277