Address review: drop modulePrefix from scenario app

modulePrefix was only ever read by Namespace#toString for debug names,
not by the strict resolver itself — the resolver keys off relative
module paths. Dropping it alongside the unused config import keeps
the scenario honest about what the strict resolver actually needs
from an app.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: NullVoxPopuli

smoke-tests/scenarios/strict-resolver-substates-test.ts

@@ -20,11 +20,8 @@ strictAppScenarios
         'app.js': `
           import Application from '@ember/application';
           import Router from './router';
-          import config from 'v2-app-template/config/environment';
 
           export default class App extends Application {
-            modulePrefix = config.modulePrefix;
-
             modules = {
               './router': { default: Router },
               ...import.meta.glob('./services/**/*.{js,ts}', { eager: true }),