Resolve "Remove unused code in core-encoder: VBR and CAM"

• Related issues: #2299 (closed)
• Requested reviewers: @vaillancour

Reason why this change is needed

• In IVAS, VBR and CAM modes are not supported and the related code can be removed.

Description of the change

• Remove unused VBR and CAM code.
• Removes cca 1,100 lines of source code.

Affected operating points

• All is BE.