In `ivas_core_encoder_fx()`, there exist two variants of SHB speech buffers for ACELP BWE processing: one in 16-bit, the other in 32-bit. These buffers involve operations where a 16-bit buffer is scaled to a temporary 32-bit buffer and then scaled back to 16-bit buffer without any processing in between. Thus, the 32-bit buffers and the scaling can be removed in a BE manner. <!--- Below are labels that will be added but are not shown in description. This is a template to help fill them. Add further information to the first row and remove and add labels as necessary.-->