zstreamdump: replace with link to zstream

zstreamdump(8) was in quite a bad state,
and the wrapper didn't work if invoked without /sbin in $PATH

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12015