Rollup merge of #134251 - bjorn3:various_cleanups2, r=oli-obk

A bunch of cleanups (part 2)

Just like https://github.com/rust-lang/rust/pull/133567 these were all found while looking at the respective code, but are not blocking any other changes I want to make in the short term.

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -12,7 +12,6 @@
 #![warn(unused_lifetimes)]
 // tidy-alphabetical-end
 
-extern crate jobserver;
 #[macro_use]
 extern crate rustc_middle;
 extern crate rustc_abi;