Remove DS import in utils

We now depend on `@ember-data/model/-private` for `ManyArray` and `PromiseManyArray` and do the ember-data feature detection by checking if `Model` from `@ember-data/model` is present.

addon/utils/utils.js

@@ -4,6 +4,8 @@ import { isHTMLSafe } from '@ember/template';
 import EmberObject from '@ember/object';
 import { typeOf } from '@ember/utils';
 import { A as emberArray } from '@ember/array';
+
+// ember-data feature detection
 import require from 'require';
 
 function requireModule(module, exportName = 'default') {
@@ -12,9 +14,24 @@ function requireModule(module, exportName = 'default') {
   }
 }
 
-const DS = requireModule('ember-data');
 const Model = requireModule('@ember-data/model');
+const { ManyArray, PromiseManyArray } = requireModule(
+  '@ember-data/model/-private'
+);
+
+export function isDsModel(o) {
+  return !!(Model && o && o instanceof Model);
+}
+
+export function isDSManyArray(o) {
+  return !!(
+    Model &&
+    o &&
+    (o instanceof PromiseManyArray || o instanceof ManyArray)
+  );
+}
 
+// ember internals
 export { getDependentKeys, isDescriptor } from '../-private/ember-internals';
 
 export function unwrapString(s) {
@@ -43,18 +60,6 @@ export function isPromise(p) {
   return !!(p && canInvoke(p, 'then'));
 }
 
-export function isDsModel(o) {
-  return !!(Model && o && o instanceof Model);
-}
-
-export function isDSManyArray(o) {
-  return !!(
-    DS &&
-    o &&
-    (o instanceof DS.PromiseManyArray || o instanceof DS.ManyArray)
-  );
-}
-
 export function isEmberObject(o) {
   return !!(o && o instanceof EmberObject);
 }