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