Fix SensioDistributionBundle#669: remove app/SymfonyRequirements.php and app/check.php in case of new directory structure

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony-standard/issues/669, #141
| License       | MIT