Auto merge of #370 - dtolnay:expand, r=erickt

Use serde_codegen::expand in serde_tests/build.rs

serde_tests/build.rs

@@ -13,10 +13,6 @@ fn main() {
     ] {
         let src = Path::new(src);
         let dst = Path::new(&out_dir).join(dst);
-
-        let mut registry = syntex::Registry::new();
-
-        serde_codegen::register(&mut registry);
-        registry.expand("", &src, &dst).unwrap();
+        serde_codegen::expand(&src, &dst).unwrap();
     }
 }