rustdoc: don't call into_iter() on iterator. (clippy::identity_conversion)

src/librustdoc/html/markdown.rs

@@ -870,7 +870,7 @@ pub fn plain_summary_line(md: &str) -> String {
     }
     let mut s = String::with_capacity(md.len() * 3 / 2);
     let p = ParserWrapper { inner: Parser::new(md), is_in: 0, is_first: true };
-    p.into_iter().filter(|t| !t.is_empty()).for_each(|i| s.push_str(&i));
+    p.filter(|t| !t.is_empty()).for_each(|i| s.push_str(&i));
     s
 }