Remove double return in mixin, refs #314

Author: shadowhand

bin/src/MixinGenerator.php

@@ -439,10 +439,7 @@ private function phpdoc(array $lines, int $indent): string
             }
         }
 
-        $phpdoc .= "\n".$indentation.' * @return void';
-
         if (strlen($throws) > 0) {
-            $phpdoc .= "\n".$indentation.' *';
             $phpdoc .= $throws;
         }