refactor: remove uneeded unset()

Author: kenjis

system/Validation/Validation.php

@@ -345,8 +345,6 @@ private function processIfExist(string $field, $rules, ?array $data)
                 $dataIsExisting = array_key_exists($ifExistField, $flattenedData);
             }
 
-            unset($ifExistField, $flattenedData);
-
             if (! $dataIsExisting) {
                 // we return early if `if_exist` is not satisfied. we have nothing to do here.
                 return true;