[RFC] merge check.php and SymfonyRequirements.php and put it under bin

this way we do not have to bother where to put the SymfonyRequirements.php file
Actually I think it's not a problem. The file will get updated when the devs remove it locally and otherwise stays as-is. This is the same for `bin/console` and I didn't like the automatic update of SymfonyRequirements.php inside the app folder anyway as it could potentially overwrite custom stuff.