simplify how the hir_typeck_pass_to_variadic_function diagnostic is created

compiler/rustc_hir_typeck/messages.ftl

@@ -146,7 +146,6 @@ hir_typeck_option_result_copied = use `{$def_path}::copied` to copy the value in
 
 hir_typeck_pass_to_variadic_function = can't pass `{$ty}` to variadic function
     .suggestion = cast the value to `{$cast_ty}`
-    .help = cast the value to `{$cast_ty}`
     .teach_help = certain types, like `{$ty}`, must be casted before passing them to a variadic function, because of arcane ABI rules dictated by the C standard
 
 hir_typeck_ptr_cast_add_auto_to_object = adding {$traits_len ->

compiler/rustc_hir_typeck/src/errors.rs

@@ -789,11 +789,8 @@ pub(crate) struct PassToVariadicFunction<'a, 'tcx> {
     pub span: Span,
     pub ty: Ty<'tcx>,
     pub cast_ty: &'a str,
-    #[suggestion(code = "{replace}", applicability = "machine-applicable")]
-    pub sugg_span: Option<Span>,
-    pub replace: String,
-    #[help]
-    pub help: bool,
+    #[suggestion(code = " as {cast_ty}", applicability = "machine-applicable", style = "verbose")]
+    pub sugg_span: Span,
     #[note(hir_typeck_teach_help)]
     pub(crate) teach: bool,
 }

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -440,20 +440,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     ty: Ty<'tcx>,
                     cast_ty: &str,
                 ) {
-                    let (sugg_span, replace, help) =
-                        if let Ok(snippet) = sess.source_map().span_to_snippet(span) {
-                            (Some(span), format!("{snippet} as {cast_ty}"), false)
-                        } else {
-                            (None, "".to_string(), true)
-                        };
-
                     sess.dcx().emit_err(errors::PassToVariadicFunction {
                         span,
                         ty,
                         cast_ty,
-                        help,
-                        replace,
-                        sugg_span,
+                        sugg_span: span.shrink_to_hi(),
                         teach: sess.teach(E0617),
                     });
                 }