remove code for Cookie List Opt-In if no longer needed

[LaurenWags]

While testing #39083 (comment) had a discussion with @mkarolin re: Cookie List Opt-In code. This dialog is no longer used as the original implementation was superseded by a subsequent issue/PR to enable the Cookie List by default. Confirmed by @rebron.

@mkarolin suggested we may want to remove the code that is no longer needed for the Cookie List Opt-In webui - it was modified as a result of the Chromium 128 upgrade and so we are maintaining code that is no longer used which does not seem like a good use of time/resources.