Fix duplication of function ivas_init_dec_get_num_cldfb_instances

Issue: #1860 (closed)

Same thing as with !1983 (merged). Fix duplication of ivas_init_dec_get_num_cldfb_instances by removing the _ivas_fx variant.

The current fix does not include switches. I can add them but would prefer not as changes are clearer for humans and git without doing so. My intention is to also rename the function to _fx-variant before merging but diff is easier to see for review without the change.

Adding @vaclav for review but also @multrus, @tyagiri, etc. could take a look.