Remove ender references in documentation and comments

It's been [pointed out](https://github.com/cameronmcefee/plax/issues/42) by @magebarf that Ender support is likely broken. Since I'm not actively working to promote Ender support, this removes documented indications that it ought to work with Ender. The Ender related code still exists, but I think that should be extracted in a different pull. I've left the `package.json` file in for now.