DEV: Switch off of our image_optim fork (PR #13124)

The main image_optim gem now includes the timeout feature that we had in our fork. So it is now safe to switch off of our fork and back to the image_optim gem.

This is the link to the commit in the image_optim repo that adds the timeout option:

One difference with the new timeout implementation is that image_optim now handles the timeout exceptions instead of bubbling them up:

 rescue Errors::TimeoutExceeded

So a timeout will just return nil, which is the same response if it couldn’t optimize an image. I don’t think we were really watching for or doing anything about these timeout warnings in our logs so I think this is an okay change to have and we will have less warnings in our logs now too.