Removes temp rake task as its served its purpose
Removes temp rake task as its served its purpose

This tasks was merged [here](https://github.com/alphagov/collections-publisher/pull/1104) and has been run in production
so we can now remove it.

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

alphagov/collections-publisher,alphagov/collections-publisher,alphagov/collections-publisher