Close #12459: Remove unused enum PARK_LOAD_ERROR (#12590)

* Remove unused enum PARK_LOAD_ERROR

A refactoring a couple of years ago removed all uses so it
can safely be removed.

Closes #12459

* Also fix header order for clang-format

src/openrct2/ParkImporter.h

@@ -10,18 +10,8 @@
 #pragma once
 
 #include "common.h"
-#include "object/Object.h"
-
-enum PARK_LOAD_ERROR
-{
-    PARK_LOAD_ERROR_OK,
-    PARK_LOAD_ERROR_MISSING_OBJECTS,
-    PARK_LOAD_ERROR_INVALID_EXTENSION,
-    PARK_LOAD_ERROR_UNSUPPORTED_RCTC_FLAG,
-    PARK_LOAD_ERROR_UNKNOWN = 255
-};
-
 #include "core/String.hpp"
+#include "object/Object.h"
 
 #include <memory>
 #include <string>