Unify the configuration of the compiler docs

Previously it was rather inconsistent which crates got the rust logo and
which didn't and setting html_root_url was forgotten in many cases.

compiler/rustc_llvm/src/lib.rs

@@ -1,9 +1,5 @@
 // tidy-alphabetical-start
-#![allow(internal_features)]
-#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![doc(rust_logo)]
 #![feature(extern_types)]
-#![feature(rustdoc_internals)]
 // tidy-alphabetical-end
 
 use std::cell::RefCell;