Functions renaming after NONBE_UNIFIED_DECODING_PATHS

After NONBE_UNIFIED_DECODING_PATHS was introduced, many function names do not really match the functionality and should be corrected:

• ivas_jbm_dec_tc() -> should be renamed to ivas_dec() and moved to ivas_dec.c
• ivas_jbm_dec_render() -> ivas_dec_render() and moved to ivas_dec.c
• ivas_omasa_separate_object_render_jbm() -> ivas_omasa_separate_object_render()
• etc.

Then, several functions have in their name _jbm_ while they are called in both non-JBM and JBM modes. It is proposed to rename these functions.

In addition, there are other leftovers after NONBE_UNIFIED_DECODING_PATHS was accepted, e.g. unnecessary functions, unnecessary dereferencing, outdated or wrong comments, duplicated or dead code, or JBM leftovers in ivas_dec().