Fix clippy::needless_borrow in the compiler

`x clippy compiler -Aclippy::all -Wclippy::needless_borrow --fix`.

Then I had to remove a few unnecessary parens and muts that were exposed
now.

compiler/rustc_codegen_ssa/src/assert_module_sources.rs

@@ -149,7 +149,7 @@ impl<'tcx> AssertModuleSource<'tcx> {
 
         self.cgu_reuse_tracker.set_expectation(
             cgu_name,
-            &user_path,
+            user_path,
             attr.span,
             expected_reuse,
             comp_kind,