loader: zfs_cmd.c does not really compile without libzfs.h

Having libzfs.h wrapped in LOADER_ZFS_SUPPORT check does not really make sense,
because we do need function declarations with C99.

Sponsored by:	Netflix, Klara Inc.

stand/common/zfs_cmd.c

@@ -37,10 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/reboot.h>
 
 #include "bootstrap.h"
-
-#ifdef LOADER_ZFS_SUPPORT
 #include "libzfs.h"
-#endif
 
 COMMAND_SET(lszfs, "lszfs", "list child datasets of a zfs dataset",
 	    command_lszfs);