revert(api): decouple api from curriculum

This reverts commit c077ffe4b9
via PR #40703

api-server/server/utils/cast-to-observable.js

@@ -0,0 +1,11 @@
+import { Observable, helpers } from 'rx';
+
+export default function castToObservable(maybe) {
+  if (Observable.isObservable(maybe)) {
+    return maybe;
+  }
+  if (helpers.isPromise(maybe)) {
+    return Observable.fromPromise(maybe);
+  }
+  return Observable.of(maybe);
+}