Revert "DEV: enforces ember-template-lint: no-triple-curlies (#9150)"

This reverts commit d436b600fb.

Triple curlies are still necessary for some raw templates.

test/javascripts/components/html-safe-helper-test.js.es6

@@ -1,14 +0,0 @@
-import componentTest from "helpers/component-test";
-moduleForComponent("html-safe-helper", { integration: true });
-
-componentTest("default", {
-  template: "{{html-safe string}}",
-
-  beforeEach() {
-    this.set("string", "<p class='cookies'>biscuits</p>");
-  },
-
-  async test(assert) {
-    assert.ok(exists("p.cookies"), "it displays the string as html");
-  }
-});

test/javascripts/lib/computed-test.js.es6

@@ -5,8 +5,7 @@ import {
   propertyNotEqual,
   fmt,
   i18n,
-  url,
-  htmlSafe
+  url
 } from "discourse/lib/computed";
 
 QUnit.module("lib:computed", {
@@ -155,12 +154,3 @@ QUnit.test("url", assert => {
     "it supports urls with a prefix"
   );
 });
-
-QUnit.test("htmlSafe", assert => {
-  const cookies = "<p>cookies and <b>biscuits</b></p>";
-  const t = EmberObject.extend({
-    desc: htmlSafe("cookies")
-  }).create({ cookies });
-
-  assert.equal(t.get("desc").string, cookies);
-});