ESLint: Enable ember/no-mixins rule

Author: Turbo87

.eslintrc.js

@@ -18,7 +18,6 @@ module.exports = {
 
     'ember/no-empty-attrs': 'off',
     'ember/no-get': 'off',
-    'ember/no-mixins': 'off',
     'ember/require-computed-property-dependencies': 'off',
 
     'import-helpers/order-imports': [