The pointer was asigned only once with vp9_regular_quantize_b_4x4, calling
this function directly now. Also removing unused declarations:
  prototype_quantize_block
  prototype_quantize_block_pair
  prototype_quantize_mb
  vp9_regular_quantize_b_4x4_pair
  vp9_regular_quantize_b_8x8

Change-Id: I14325bc2f082336820671eafbc06126651b79f73