Fix a man page link in zfs-program.8

zfs-program.8 has an orphan link, fix it.

https://svnweb.freebsd.org/base?view=revision&revision=360080

Obtained from: FreeBSD
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alan Somers <asomers@gmail.com>
Closes #11529