[PNG] WPT late eXIf test

Hello everyone,

In our last meeting, I signed up to add a test to confirm when EXIF data
arrives too late in the data stream it is ignored.

We knew there was an existing test for eXIf in a PNG. I was going to modify
that image and test.

But it looks like the test already covers both cases:
https://github.com/web-platform-tests/wpt/blob/master/css/css-images/image-orientation/image-orientation-exif-png.html

I believe the eXIf tests are covered as a result.