Remove unsupported ember from ember-try.js

Author: NullVoxPopuli

test-app/config/ember-try.js

@@ -7,14 +7,6 @@ module.exports = async function () {
   return {
     usePnpm: true,
     scenarios: [
-      {
-        name: 'ember-lts-3.28',
-        npm: {
-          devDependencies: {
-            'ember-source': '~3.28.0',
-          },
-        },
-      },
       {
         name: 'ember-lts-4.4',
         npm: {