Knowledge Alpha content type appears to be obsolete

[chao-xian]

I found https://content-data.publishing.service.gov.uk/metrics/knowledge-alpha

which says there's a content type of knowledge_alpha

It was added in 2018 https://github.com/alphagov/govuk-content-schemas/blob/main/formats/knowledge_alpha.jsonnet

No page exists and the URL associated with it is a 404. Should we get rid of it?