Remove `versioned` attribute from Resource interface

[victorlin]

Description of proposed changes

This attribute only served as an alias to determine if the optional attributes firstUpdated|dates|nVersions|updateCadence are available. It's more direct (and preferred by the compiler) to check for presence of the individual attributes directly where needed.

versioned at the top level on ListResourcesResponsiveProps is still valuable and should be kept.

Related issue(s)

• follow-up to https://github.com/nextstrain/nextstrain.org/pull/874#discussion_r1626764829

Checklist

• [x] Preview: /pathogens and /staging look normal (apart from #896)
• [x] Checks pass
• [x] ~Check if changes affect the resource index JSON revision~

[victorlin]

Added testing notes in the PR checklist.