Remove unused BLOCK member force_empty

Change-Id: I72ed49ce14ca0124dd0d31bfcf4c7630a4681587

vp8/encoder/block.h

@@ -45,10 +45,6 @@ typedef struct
     unsigned char **base_src;
     int src;
     int src_stride;
-
-//  MV  enc_mv;
-    int force_empty;
-
 } BLOCK;
 
 typedef struct

vp8/encoder/ethreading.c

@@ -350,8 +350,6 @@ static void setup_mbby_copy(MACROBLOCK *mbdst, MACROBLOCK *mbsrc)
         z->block[i].src             = x->block[i].src;
         */
         z->block[i].src_stride       = x->block[i].src_stride;
-        z->block[i].force_empty      = x->block[i].force_empty;
-
     }
 
     {