Remove duplicated code in core-coder: non-linearity and LP-CNG

• Related issues: #2345 (closed)
• Requested reviewers:

Reason why this change is needed

• Duplicated code in core-coder: non-linearity and LP-CNG

Description of the change

• Remove duplicated code in core-coder: non-linearity and LP-CNG.
• Removes cca 1,900 lines of the source code.

Affected operating points

• All is BE.

Closes #2345 (closed)