Remove unused Clean impl for Rc<T>

Author: camelid

src/librustdoc/clean/mod.rs

@@ -33,7 +33,6 @@ use std::assert_matches::assert_matches;
 use std::collections::hash_map::Entry;
 use std::default::Default;
 use std::hash::Hash;
-use std::rc::Rc;
 use std::{mem, vec};
 
 use crate::core::{self, DocContext, ImplTraitParam};
@@ -61,12 +60,6 @@ impl<T: Clean<U>, U> Clean<U> for &T {
     }
 }
 
-impl<T: Clean<U>, U> Clean<U> for Rc<T> {
-    fn clean(&self, cx: &mut DocContext<'_>) -> U {
-        (**self).clean(cx)
-    }
-}
-
 impl Clean<Item> for doctree::Module<'_> {
     fn clean(&self, cx: &mut DocContext<'_>) -> Item {
         let mut items: Vec<Item> = vec![];