Unused functions and related Makefile warning settings

There are some unused static functions in the code, namely:

• - static int16_t ivas_qmetadata_entropy_encode_diffuseness_hr(), lib_enc/ivas_qmetadata_enc.c:1463:16 -> @vasilache and/or @weckbecker
• - static void set_f(), lib_debug/snr.c:87:13 -> I don't know who is the original author of the debug functions. There is another set_f function in the framework, though, so I guess it is fine to remove. @malenovsky
• - static int16_t IVAS_DEC_VoIP_GetRenderGranularity(), lib_dec/lib_dec.c:3620:16 -> @bayers is this a remnant from the time where we had both 20 and 5ms rendering granularity?
• - static CREND_WRAPPER defaultCrendWrapper(),lib_rend/lib_rend.c:1281:22 -> @emerit @lefort @tamarapu @pihlajakuja (rendering folks + especiall Orange colleagues)
• IVAS_REND_GetMainOrientation(), IVAS_REND_GetTrackedRotation(), IVAS_REND_GetCombinedOrientation() -> @bayers

I stumbled about this randomly. Currently, there is explicitly done "-Wno-unused-function" which prevents this kind of warnings. Maybe this was helpful once, maybe we want to add this warnings back and remove the corresponding functions.