Remove duplicated code: FD BWE
The core-coder duplicates several FD BWE-related functions. This issue is to track the removal of duplications in functions such as:
- wb_bwe_enc_ivas_fx() vs wb_bwe_enc_fx()
- swb_bwe_enc_ivas_fx() vs swb_bwe_enc_fx()
- WB_BWE_encoding_ivas_fx() vs WB_BWE_encoding_fx()
- SWB_BWE_encoding_ivas_fx() vs SWB_BWE_encoding_fx()