chore: remove unused crate::utils::format_auto

Using `HeaderPart::auto` for formatting instead.

Author: ytmimi

src/utils.rs

@@ -117,16 +117,6 @@ pub(crate) fn format_safety(unsafety: ast::Safety) -> &'static str {
     }
 }
 
-// FIXME(ytmimi) might want to get rid of `format_auto` since we now have `HeaderPart::auto`
-#[allow(unused)]
-#[inline]
-pub(crate) fn format_auto(is_auto: ast::IsAuto) -> &'static str {
-    match is_auto {
-        ast::IsAuto::Yes => "auto ",
-        ast::IsAuto::No => "",
-    }
-}
-
 #[inline]
 pub(crate) fn format_mutability(mutability: ast::Mutability) -> &'static str {
     match mutability {