Remove function that become unused after refactoring in
e2af2acce3.
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Libby <rlibby@FreeBSD.org>
Closes#11614