Remove unused define.

Suggested by 罗泽轩.

src/lj_def.h

@@ -80,7 +80,6 @@ typedef unsigned int uintptr_t;
 #define LJ_MIN_SBUF	32		/* Min. string buffer length. */
 #define LJ_MIN_VECSZ	8		/* Min. size for growable vectors. */
 #define LJ_MIN_IRSZ	32		/* Min. size for growable IR. */
-#define LJ_MIN_K64SZ	16		/* Min. size for chained K64Array. */
 
 /* JIT compiler limits. */
 #define LJ_MAX_JSLOTS	250		/* Max. # of stack slots for a trace. */