syntax: remove #![feature(box_syntax, box_patterns)]

src/libsyntax/ext/source_util.rs

@@ -128,7 +128,7 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree
         }
     }
 
-    box ExpandResult { p: p }
+    Box::new(ExpandResult { p: p })
 }
 
 // include_str! : read the given file, insert it as a literal string expr