Remove the body.map(), body transformer and related types

[gestchild]

Once we've completed #10780, we should be able able to rely on the SliceZone to render the body slices.

We can then:

• remove the toggle
• remove the body.map() from Body.tsx
• remove the body transformer
• remove @weco/content/services/prismic/types/body as we now get these from '@weco/common/prismicio-types'; (need to fix the ContactSlice type first)