[SD-495] remove site section theming

[lambry]

Issue: https://digital-vic.atlassian.net/browse/SD-495

What I did

• Remove site section theming

Checklist

For all PR's

• I've added relevant changes to the project Readme if needed
• I've updated the documentation site as needed
• I have added tests to cover my changes (if not applicable, please state why in a comment)

For new UI components only

• I have added a storybook story covering all variants
• I have checked a11y tab in storybook passes
• I have added cypress component tests (if the component is interactive)
• Any events are emitted on the event bus using emitRplEvent