Fix author lint and move it back to tests/ui

The author lint is not an internal lint, and should also be enabled, when Clippy
is distributed through rustup. This moves the author lint test cases back to
tests/ui.

tests/ui/author.rs

@@ -1,5 +1,3 @@
-#![warn(clippy::author)]
-
 fn main() {
     #[clippy::author]
     let x: char = 0x45 as char;