Fix new-style request leak
Fix new-style request leak

The new request style was leaking channels in the respMap when requests
timed out. Now we remove them from the map when the request times out.

This also simplifies the respMux setup and prevents multiple resp
subscriptions from being created on the server.

ZebinKang/go-nats,wallyqs/go-nats,nats-io/nats,nats-io/nats,apcera/nats,ZebinKang/go-nats,nats-io/go-nats,nats-io/go-nats,apcera/nats,wallyqs/go-nats