Remove empty function vp9_build_block_offsets

This function is empty, hence is removed.

Change-Id: Ia9d01710806bffe0398a6dc9405f8a5a81b27d74

vp9/encoder/vp9_firstpass.c

@@ -521,8 +521,6 @@ void vp9_first_pass(VP9_COMP *cpi) {
 
   xd->mode_info_context = cm->mi;
 
-  vp9_build_block_offsets(x);
-
   vp9_setup_block_dptrs(&x->e_mbd, cm->subsampling_x, cm->subsampling_y);
 
   vp9_frame_init_quantizer(cpi);