Remove useless test header setup for emails

Once upon a time we needed a helper to set the `from` header of emails.
This is now set in the ApplicationMailer and not necessary any more.

spec/support/email_helper.rb

@@ -2,12 +2,6 @@
 
 module OpenFoodNetwork
   module EmailHelper
-    # Some specs trigger actions that send emails, for example creating an order.
-    # But sending emails doesn't work out-of-the-box. This code sets it up.
-    def setup_email
-      Spree::Config[:mails_from] = "test@ofn.example.org"
-    end
-
     # Ensures the value `perform_deliveries` had is restored. This saves us
     # from messing up with the test suite's global state which is cause of
     # trouble.