Removes redundant route
Removes redundant route

Depends on:
https://github.com/alphagov/collections-publisher/pull/1102 & https://github.com/alphagov/router-api/pull/337.

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Trello:
https://trello.com/c/Fi2Z2zDy/399-redirect-and-remove-legacy-email-signup-routes-for-collections

alphagov/collections,alphagov/collections,alphagov/collections,alphagov/collections