Fix WX_ASSERT_SAME_AS_FILE() definition in the new drawing test.

This macro should use AreFilesContentsEqual(), not
AreImagesFilesContentsEqual(), used by WX_ASSERT_SAME_AS_IMAGE_FILE().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76168 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775