Remove `DEPRECATED` fields from prismic

[onmax]

Following #123, once the migration is complete, we should remove all fields in Prismic that are marked as DEPRECATED. This includes reviewing the slicemachine and codebase to ensure deprecated fields are fully cleaned up.

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Tasks

1. Go through each page in Prismic and confirm no DEPRECATED fields are in use
2. Remove deprecated fields from the slicemachine definitions
3. Delete related code references that rely on these deprecated fields

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Example:
The SimpleHeadline slice includes a cta prop marked as deprecated, but it’s still present in the code. This should be safely removed.

Why:
Reduces technical debt and avoids confusion for future updates.