Remove unnecessary code for CookieBanner

Description

As part of adding CookieBanner in this repo, we copied code verbatim from AP Frontend.

Not all of that code is relevant; we should remove all unnecessary code. The only code that is necessary is code that enables the acceptance criteria for this feature. (Which we should cement, before moving forward.)

Further details

Acceptance criteria is approximately:

Feature: CookieBanner
  As a developer
  I want to be able to add a style-conformant banner to a React app
  And that banner needs to prompt end users about their cookie preferences

  Scenario: Prompted if no cookie preferences set

  Scenario: Cookie preferences are stored with TTL

  Scenario: Clearing cookies clears cookie preferences

Task list

Acceptance criteria

• Functionality of CookieBanner is as before, but unused code is removed.

Links/references