Remove stage0 stuff that was awaiting snapshot

and re-register snapshots

Just removing unneeded code, no review

src/libstd/json.rs

@@ -273,32 +273,6 @@ pub impl PrettySerializer: serialization::Serializer {
     }
 }
 
-#[cfg(stage0)]
-pub impl Json: serialization::Serializable {
-    fn serialize<S: serialization::Serializer>(&self, s: &S) {
-        match *self {
-            Number(v) => v.serialize(s),
-            String(ref v) => v.serialize(s),
-            Boolean(v) => v.serialize(s),
-            List(v) => v.serialize(s),
-            Object(ref v) => {
-                do s.emit_rec || {
-                    let mut idx = 0;
-                    for v.each |key, value| {
-                        do s.emit_field(*key, idx) {
-                            value.serialize(s);
-                        }
-                        idx += 1;
-                    }
-                }
-            },
-            Null => s.emit_nil(),
-        }
-    }
-}
-
-#[cfg(stage1)]
-#[cfg(stage2)]
 pub impl<
     S: serialization::Serializer
 > Json: serialization::Serializable<S> {