Unused variables within HR_METADATA

The Linux build returns the following warnings:

/builds/rep/ivas-codec-pc/ivas-codec/lib_dec/ivas_qmetadata_dec.c:817:13: warning: variable 'bits_diff_sum' set but not used [-Wunused-but-set-variable]
    int16_t bits_diff_sum;
            ^
/builds/rep/ivas-codec-pc/ivas-codec/lib_dec/ivas_qmetadata_dec.c:821:13: warning: variable 'bits_no_dirs_coh' set but not used [-Wunused-but-set-variable]
    int16_t bits_no_dirs_coh, bits_sur_coherence;
            ^
/builds/rep/ivas-codec-pc/ivas-codec/lib_enc/ivas_qmetadata_enc.c:752:13: warning: variable 'bits_no_dirs_coh' set but not used [-Wunused-but-set-variable]
    int16_t bits_no_dirs_coh;
            ^