ivas_jbm_dec_tc(): remove unused code

There is an unused code in function ivas_jbm_dec_tc() which is a leftover from debugging days.

Moreover, a similar code related to a scaling logic around ivas_sba_dirac_stereo_dec() is used three times while it can be recycled.

The changes would result in ivas_jbm_dec_tc() being much more in line between float annd BASOP frameworks.