[de] Removed old text for validation.alpha_dash
[de] Removed old text for validation.alpha_dash

"Umlaute (ä, ö, ü) und Eszett (ß) sind nicht erlaubt."
They are valid in Laravel 5.4:
https://github.com/illuminate/validation/blob/5.4/Concerns/ValidatesAttributes.php#L243
overtrue-forks/Laravel-lang,idhamperdameian/Laravel-lang,overtrue-forks/Laravel-lang