Refactor before actions in dr controller
Refactor before actions in dr controller

`new_defence_request` was not needed, because the
new and create actions defence on the form, 
not a defence_request instance.

We were also manually setting the policy on `new`
and `create` for no reason.
ministryofjustice/defence-request-service,ministryofjustice/defence-request-service,ministryofjustice/defence-request-service,ministryofjustice/defence-request-service