Be more lenient with streams in the pending_send queue. (#261)

The `is_peer_reset()` check doesn't quite cover all the cases where we call
`clear_queue`, such as when we call `recv_err`. Instead of trying to make the
check more precise, let's gracefully handle spurious entries in the queue.

src/proto/streams/state.rs

@@ -325,13 +325,6 @@ impl State {
         }
     }
 
-    pub fn is_peer_reset(&self) -> bool {
-        match self.inner {
-            Closed(Cause::Proto(_)) => true,
-            _ => false,
-        }
-    }
-
     /// Returns true if the stream is already reset.
     pub fn is_reset(&self) -> bool {
         match self.inner {