Remove code for zfs remap

The "zfs remap" command was disabled by
6e91a72fe3, because it has little utility
and introduced some tricky bugs.  This commit removes the code for it,
the associated ZFS_IOC_REMAP ioctl, and tests.

Note that the ioctl and property will remain, but have no functionality.
This allows older software to fail gracefully if it attempts to use
these, and avoids a backwards incompatibility that would be introduced if
we renumbered the later ioctls/props.

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #8944

lib/libzfs/libzfs_dataset.c

@@ -4210,36 +4210,6 @@ zfs_snapshot_cb(zfs_handle_t *zhp, void *arg)
 	return (rv);
 }
 
-int
-zfs_remap_indirects(libzfs_handle_t *hdl, const char *fs)
-{
-	int err;
-	char errbuf[1024];
-
-	(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
-	    "cannot remap dataset '%s'"), fs);
-
-	err = lzc_remap(fs);
-
-	if (err != 0) {
-		switch (err) {
-		case ENOTSUP:
-			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
-			    "pool must be upgraded"));
-			(void) zfs_error(hdl, EZFS_BADVERSION, errbuf);
-			break;
-		case EINVAL:
-			(void) zfs_error(hdl, EZFS_BADTYPE, errbuf);
-			break;
-		default:
-			(void) zfs_standard_error(hdl, err, errbuf);
-			break;
-		}
-	}
-
-	return (err);
-}
-
 /*
  * Creates snapshots.  The keys in the snaps nvlist are the snapshots to be
  * created.

lib/libzfs_core/libzfs_core.c

@@ -306,16 +306,6 @@ lzc_promote(const char *fsname, char *snapnamebuf, int snapnamelen)
 	return (0);
 }
 
-int
-lzc_remap(const char *fsname)
-{
-	int error;
-	nvlist_t *args = fnvlist_alloc();
-	error = lzc_ioctl(ZFS_IOC_REMAP, fsname, args, NULL);
-	nvlist_free(args);
-	return (error);
-}
-
 int
 lzc_rename(const char *source, const char *target)
 {