Touch up new_raw workaround comment

This comment was copied verbatim from quote but that code was
substantially different. They started with a string _including_ the r#
prefix, and then used &id[2..] to obtain an unraw version of it, which
is what "unraw" in the comment refers to. The code in proc-macro2 is
doing the opposite.

src/wrapper.rs

@@ -699,9 +699,9 @@ impl Ident {
             #[cfg(no_ident_new_raw)]
             Span::Compiler(s) => {
                 let _ = proc_macro::Ident::new(string, s);
-                // At this point, the identifier is raw, and the unraw-ed version of it was
-                // successfully converted into an identifier. Try to produce a valid raw
-                // identifier by running the `TokenStream` parser, and unwrapping the first
+                // At this point the un-r#-prefixed string is known to be a
+                // valid identifier. Try to produce a valid raw identifier by
+                // running the `TokenStream` parser, and unwrapping the first
                 // token as an `Ident`.
                 let raw_prefixed = format!("r#{}", string);
                 if let Ok(ts) = raw_prefixed.parse::<proc_macro::TokenStream>() {