Remove unused ember-deferred-content addon (#1695)

Author: begedin

package.json

@@ -64,7 +64,6 @@
     "ember-composable-helpers": "2.1.0",
     "ember-concurrency": "^0.8.1",
     "ember-data": "~2.18.0",
-    "ember-deferred-content": "0.2.0",
     "ember-disable-proxy-controllers": "^1.0.1",
     "ember-dragula": "1.9.3",
     "ember-exam": "1.0.0",