Remove Default derive from MacroExpectedFound.

It's the only diagnostic in the entire project that impls `Default`, and
the code is clearer without it.

Author: nnethercote

compiler/rustc_resolve/src/errors.rs

@@ -521,7 +521,7 @@ pub(crate) struct ToolModuleImported {
 #[diag(resolve_module_only)]
 pub(crate) struct ModuleOnly(#[primary_span] pub(crate) Span);
 
-#[derive(Diagnostic, Default)]
+#[derive(Diagnostic)]
 #[diag(resolve_macro_expected_found)]
 pub(crate) struct MacroExpectedFound<'a> {
     #[primary_span]

compiler/rustc_resolve/src/macros.rs

@@ -562,7 +562,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 expected,
                 found: res.descr(),
                 macro_path: &path_str,
-                ..Default::default() // Subdiagnostics default to None
+                remove_surrounding_derive: None,
+                add_as_non_derive: None,
             };
 
             // Suggest moving the macro out of the derive() if the macro isn't Derive