[FrameworkBundle] Improved controller class error

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony/issues/11304
| License       | MIT
| Doc PR        | 
According to `FrameworkBundle`'s [composer.json](https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/FrameworkBundle/composer.json#L26), you already require `symfony/routing` component as a dependency. We're fine to use `_route` here.