Remove a bunch of (hopefully) unnecessary Pins.

I believe these were introduced previously to solve a problem that we're
no longer dealing with; specifically, if I remember correctly, we
introduced these to deal with how we were going to implement a trait.
However, they don't appear to be necessary any more, so we're going to
get rid of them, so we won't need to deal with them any longer.

src/messages/utils.rs

@@ -25,7 +25,7 @@ macro_rules! standard_roundtrip {
                 let mut buffer = vec![];
                 task::block_on(xs.write(&mut buffer)).unwrap();
                 let mut cursor = Cursor::new(buffer);
-                let ys = <$t>::read(Pin::new(&mut cursor));
+                let ys = <$t>::read(&mut cursor);
                 xs == task::block_on(ys).unwrap()
             }
         }