Revert "Rename all test files from JS -> ES6"

This reverts commit 2abe85b834.

test/javascripts/acceptance/custom-html-template-test.js

@@ -1,18 +0,0 @@
-import { acceptance } from "helpers/qunit-helpers";
-
-acceptance("CustomHTML template", {
-  beforeEach() {
-    Ember.TEMPLATES["top"] = Ember.HTMLBars.compile(
-      `<span class='top-span'>TOP</span>`
-    );
-  },
-
-  afterEach() {
-    delete Ember.TEMPLATES["top"];
-  }
-});
-
-QUnit.test("renders custom template", async assert => {
-  await visit("/static/faq");
-  assert.equal(find("span.top-span").text(), "TOP", "it inserted the template");
-});