Resolve "ivas_jbm_dec_tc(): remove unused code"

• Related issues: #2296
• Requested reviewers:

Reason why this change is needed

• There is an unused code in function ivas_jbm_dec_tc()

Description of the change

• Remove unused code in function ivas_jbm_dec_tc()
• Recycle scaling logic around ivas_sba_dirac_stereo_dec()
• correct the length of buffers that are scaled from L_FRAME48k to output_frame

Affected operating points

• All is BE.