Update test page

[Alex313031]

• Fix some minor things Also don't worry about the "delete jxl.svg" commit. This was a mistake on my part, and doesnt actually delete anything from the repo.

[goodusername123]

I'm not a web dev but couldn't the thumbnail image just be pointed to "http://jpegxl.info/jxl.png" like it is for index.html instead of there being a duplicate png on the repo/website? doing this would probably also help with browser side image caching (like I said i'm not a web dev so I could be wrong about this also).

[Alex313031]

@goodusername123 Well normally how you would do it is not via an https url. Because its not guaranteed that URL will always be there or be the same name. How you would do it is "../jxl.png" telling it to go one directory up. However, I made this change, because it is also not guaranteed someone (like me, see below) wouldn't want to deploy only parts of the website.

I deployed the test page on my own website, and doing it this way makes the test page subdir work entirely on its own as its own site. See > https://thorium.rocks/misc/jxl-test-page/