Fix more clippy warnings

Fixes more of:

clippy::unused_unit
clippy::op_ref
clippy::useless_format
clippy::needless_return
clippy::useless_conversion
clippy::bind_instead_of_map
clippy::into_iter_on_ref
clippy::redundant_clone
clippy::nonminimal_bool
clippy::redundant_closure
clippy::option_as_ref_deref
clippy::len_zero
clippy::iter_cloned_collect
clippy::filter_next

src/librustdoc/html/sources.rs

@@ -126,7 +126,7 @@ impl<'a> SourceCollector<'a> {
             &self.scx.themes,
         );
         self.scx.fs.write(&cur, v.as_bytes())?;
-        self.scx.local_sources.insert(p.clone(), href);
+        self.scx.local_sources.insert(p, href);
         Ok(())
     }
 }