clippy: fix up into_iter and clone-on-copy

Author: seanmonstar

http-body-util/src/collected.rs

@@ -53,7 +53,7 @@ impl<B: Buf> Collected<B> {
 
         if let Ok(trailers) = frame.into_trailers() {
             if let Some(current) = &mut self.trailers {
-                current.extend(trailers.into_iter());
+                current.extend(trailers);
             } else {
                 self.trailers = Some(trailers);
             }

http-body-util/src/empty.rs

@@ -57,9 +57,7 @@ impl<D> Default for Empty<D> {
 
 impl<D> Clone for Empty<D> {
     fn clone(&self) -> Self {
-        Self {
-            _marker: PhantomData,
-        }
+        *self
     }
 }