Remove /author/ from the author profile url

Essentially, you can’t do that because you’ve overlapped the “page” and “author” sections in the namespace.

See, with your setup, then given a URL like http://example.com/whatever, WordPress has no way to distinguish whether “whatever” is an author or a Page.

To do this, you’d need to add a lot more code to add extra querying during the rewrite parsing, basically. Which means that you should use a plugin to do it, if you still want to do it at all.