Remove rule about modifying posters

Suggestion to remove this rule about poster images:

If the existing display poster is incorrect – you must request a new poster to replace the current image first. Submitting a request to delete the existing 'primary' poster, before the new one is live will result in your contribution being discarded. 

In a user-contributed feature, it should always be possible to correct errors. It should not be dependent on the ability to provide a suitable image, which may not exist.

https://help.imdb.com/article/contribution/images-videos/how-do-i-update-my-poster/GA8N34CWGUMJJM98