Remove unused code in core-coder: HQ core

The core-coder duplicates several functions, namely in hq_core_[enc,dec]_fx() and hq_core_[enc,dec]_ivas_fx() there are called several functions which are duplicated or not used at all.

In IVAS HQ core, LR-HQ core and 8 kHz I/O sampling rate are not supported and the related code can be removed.