Remove st->previoussynth_fx_32[]

• Related issues: #2379 (closed)
• Requested reviewers:

Reason why this change is needed

• There is an unnecessary duplicated buffer st->previoussynth_fx_32[].

Description of the change

• Remove duplicated buffer st->previoussynth_fx_32[]. The buffer is identical to st->previoussynth_fx[] and both hold the same values in Q0.

Affected operating points

• All is BE.

Closes #2379 (closed)