fix coding style

Author: malsuke

src/Type/Php/PregSplitDynamicReturnTypeExtension.php

@@ -24,7 +24,6 @@
 use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
-use PHPStan\Type\TypeUtils;
 use function count;
 use function is_array;
 use function is_int;