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_ast/src/attr/mod.rs

@@ -391,7 +391,7 @@ impl MetaItemKind {
                 MetaItemKind::name_value_from_tokens(&mut inner_tokens.trees())
             }
             Some(TokenTree::Token(token, _)) => {
-                MetaItemLit::from_token(&token).map(MetaItemKind::NameValue)
+                MetaItemLit::from_token(token).map(MetaItemKind::NameValue)
             }
             _ => None,
         }