Sent to a WIMMessageCallback function to tell the caller how many stale files were removed.
WIM_MSG_WARNING_STALE_MOUNT_FILE wParam = (ULONG) FilesDeleted; lParam = (WCHAR) DriveLetter;
[in] A ULONG value indicating how many stale files were deleted.
[in] A WCHAR value indicating which drive letter was scanned.
Your routine must return WIM_MSG_SUCCESS.