Don't name the output of the const block

Don't name the output of the const block in which traits are
implemented. This doesn't play well with Rust RFC 3373, and isn't
necessary for correctness.

Fixes yaahc#46

src/expand.rs

@@ -19,10 +19,9 @@ pub(crate) fn derive(input: &DeriveInput) -> Result<TokenStream> {
     }?;
 
     let helpers = specialization();
-    let dummy_const = format_ident!("_DERIVE_Display_FOR_{}", input.ident);
     Ok(quote! {
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
-        const #dummy_const: () = {
+        const _: () = {
             #helpers
             #impls
         };