Merge pull request #14894 from emberjs/enable-no-double-extend

[FEATURE ember-no-double-extend] Enable by default

features.json

@@ -7,7 +7,7 @@
     "ember-glimmer-allow-backtracking-rerender": null,
     "ember-testing-resume-test": null,
     "ember-factory-for": true,
-    "ember-no-double-extend": null,
+    "ember-no-double-extend": true,
     "ember-routing-router-service": null,
     "ember-unique-location-history-state": null
   }