Remove specific filter for classnames

[swissspidy]

There isn't a project where we've actually needed the rest_likes.classnames filter.

Having this filter means we need to pass the list of class names to the JS as well, which makes things a bit more complex.

I don't think there's a need for that. We could just hardcode the classnames in the markup / JS to reduce complexity.

[swissspidy]

Oh, and of course this would make integration with Gutenberg or for example AMP easier because we can actually rely on the class names being the same instead of worrying about someone filtering them.