Remove struct POS.

It is never used.

Change-Id: If7462357c0498ed05af2645f0c272124381d3aab

vp9/common/vp9_blockd.h

@@ -45,10 +45,6 @@
 #define MAX_MV_REFS 9
 #define MAX_MV_REF_CANDIDATES 4
 
-typedef struct {
-  int r, c;
-} POS;
-
 typedef enum {
   PLANE_TYPE_Y_WITH_DC,
   PLANE_TYPE_UV,