contrib/dracut: zfs-lib: export_all: replace with inline zpool export -a

07a3312f17, which introduced this in
October of 2014, didn't have zpool export -a available; we do

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13093

contrib/dracut/90zfs/export-zfs.sh.in

@@ -1,10 +1,8 @@
 #!/bin/sh
 
-. /lib/dracut-zfs-lib.sh
-
 _do_zpool_export() {
 	info "ZFS: Exporting ZFS storage pools..."
-	errs=$(export_all -F 2>&1)
+	errs=$(zpool export -aF 2>&1)
 	ret=$?
 	echo "${errs}" | vwarn
 	if [ "${ret}" -ne 0 ]; then