Turn off FAST_OPTIMIZE_TXB

This mode introduces bug that causes lv_map having performance
drop when turning on optimize_txb in rd loop.

I will fix the bug and turn this back on.

Change-Id: I5d2f8d2f8e5b9529a2fd23f4679bcb16de259f73

av1/encoder/encodetxb.c

@@ -1199,7 +1199,7 @@ static INLINE int check_br_neighbor(tran_low_t qc) {
   return abs(qc) > BR_MAG_OFFSET;
 }
 
-#define FAST_OPTIMIZE_TXB 1
+#define FAST_OPTIMIZE_TXB 0
 
 #if FAST_OPTIMIZE_TXB
 #define ALNB_REF_OFFSET_NUM 2