Fix not removing readers in file upload example

[mc1098]

Description

A bit of deja vu for you but this fixes the same issue as #2054 but on master :)

In the file upload example we store the FileReaders while reading from
the uploaded file but once read we never remove them from the vec.

Closes #2035

Checklist

• I have run cargo make pr-flow
• I have reviewed my own code
• I have added tests

[allsey87]

Definitely better than just indefinitely leaving them in a Vec<_>, but I am thinking that this could cause problems if one were to try uploading a directory containing multiple FILENAME.EXT, that is, in different subdirectories...

[mc1098]

My understanding is that you can't select directories without the webkitdirectory attribute which is not standard. So I think this is okay, though it was interesting because I didn't even know about webkitdirectory 😅. If / when it becomes standard then we might have to review this example again.

[mc1098]

Happy to merge? :)

[siku2]

If you don't want to press the button, I certainly enjoy doing so :P