revert(api): decouple api from curriculum

This reverts commit c077ffe4b9
via PR #40703

api-server/common/models/article.js

@@ -0,0 +1,9 @@
+import { Observable } from 'rx';
+
+module.exports = function(Article) {
+  Article.on('dataSourceAttached', () => {
+    Article.findOne$ = Observable.fromNodeCallback(Article.findOne, Article);
+    Article.findById$ = Observable.fromNodeCallback(Article.findById, Article);
+    Article.find$ = Observable.fromNodeCallback(Article.find, Article);
+  });
+};