zfs: no need to check that size of zfs_cmd_t is not greater than IOCPARM_MAX

Nowadays we do not pass zfs_cmd_t directly through the ioctl interface.
Instead a small zfs_iocparm_t object is passed and the command is
explicitly copied in and out.  So, the check has become irrelevant.

MFC after:	3 weeks
Sponsored by:	Panzura

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c

@@ -204,7 +204,6 @@
 #include "lua.h"
 #include "lauxlib.h"
 
-CTASSERT(sizeof(zfs_cmd_t) < IOCPARM_MAX);
 static struct cdev *zfsdev;
 
 extern void zfs_init(void);