doc(utils): remove the work-around now that the compiler bug has been fixed

It might have been fixed by [1], but I'm not entirely sure.

[1]: rust-lang/rust#77862

Author: yvt

src/r3/src/utils/intrusive_list.rs

@@ -467,7 +467,6 @@ where
             return Err(ItemError::NotLinked);
         }
 
-        #[doc(hidden)] // FIXME: This macro somehow appears on rustdoc
         macro on_inconsistency() {{
             // If the closure body refers to `self`, the closure would capture
             // the whole `self` by reference, which conflicts with mutable