[Console] Removing unnecessary sprintf in Application->getHelp

Minor change of the `Symfony\Component\Console\Application->getHelp()`  method.

I have spotted:
1. an unnecessary `sprintf` call (no `args` arguments);
2. two ways of adding a new line in the help (an empty string as new entry of the array and a `\n` at the end of the string).

It seems to be there since the begining and it looks like a forgoten change to me, so I fixed them by removing the `sprintf` call and using a new array entry (empty string) instead of the `\n`.

| Q             | A
| ------------- | ---
| License       | MIT