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.

Author: bjorn3

compiler/rustc_public/src/lib.rs

@@ -7,10 +7,7 @@
 //! This API is still completely unstable and subject to change.
 
 #![allow(rustc::usage_of_ty_tykind)]
-#![doc(
-    html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
-    test(attr(allow(unused_variables), deny(warnings)))
-)]
+#![doc(test(attr(allow(unused_variables), deny(warnings))))]
 #![feature(sized_hierarchy)]
 //!
 //! This crate shall contain all type definitions and APIs that we expect third-party tools to invoke to