Removed unnecessary bookshelf-relations config in EmailRecipient model

no issue

- we don't use any of the `bookshelf-relations` plugin's added features for the `EmailRecipient` model so there's no need to opt in to it

core/server/models/email-recipient.js

@@ -4,12 +4,6 @@ const EmailRecipient = ghostBookshelf.Model.extend({
     tableName: 'email_recipients',
     hasTimestamps: false,
 
-    relationships: ['email'],
-
-    relationshipBelongsTo: {
-        email: 'emails'
-    },
-
     email() {
         return this.belongsTo('Email', 'email_id');
     },