message: Fix new clippy warnings since Rust 1.57
diff: @@ -1049,10 +1049,10 @@ fn generate_function_pointers<'a>(
  let pfn_typedefs = commands
  .iter()
  .filter(|pfn| pfn.type_needs_defining)
  - .map(|pfn| CommandToType(pfn));
  - let members = commands.iter().map(|pfn| CommandToMember(pfn));
  - let loaders = commands.iter().map(|pfn| CommandToLoader(pfn));
  - let bodies = commands.iter().map(|pfn| CommandToBody(pfn));
  + .map(CommandToType);
  + let members = commands.iter().map(CommandToMember);
  + let loaders = commands.iter().map(CommandToLoader);
  + let bodies = commands.iter().map(CommandToBody);
  quote! {
  #(#pfn_typedefs)*
  