test: Remove inverse relation in auth-method

ui/core/mirage/config.js

@@ -64,7 +64,7 @@ export default function() {
     const account = accounts.find(id);
     const updatedAttrs = {
       version: attrs.version,
-      attributes: {}
+      attributes: account.attributes
     };
     // Set new password
     if (method === 'set-password') {

ui/core/mirage/models/auth-method.js

@@ -2,7 +2,6 @@ import { Model, belongsTo, hasMany} from 'ember-cli-mirage';
 
 export default Model.extend({
 
-  scope: belongsTo(),
-  accounts: hasMany('account')
+  scope: belongsTo()
 
 });