Remove duplicated code: gauss_L2_ivas_fx()

• Related issues: #2424
• Requested reviewers:

Reason why this change is needed

• The core-coder duplicates functions gauss_L2_fx() and gauss_L2_fx().

Description of the change

• Remove duplication of gauss_L2_fx() and gauss_L2_fx().

Affected operating points

• All is BE.

Closes #2424