Update to use @grpc/grpc-js node package, and update helloworld example

[stanley-cheung]

With the 1.0 release of @grpc/grpc-js and the announcement that the original grpc node package will not receive new features, let's update our usage to the @grpc/grpc-js package.

In the process, I made some cleanups to the helloworld example.

• The helloworld example server.js needs to use bindAsync instead of bind
• I removed the deadline exceeded example to keep the helloworld example simple. (Technically, even the streaming example for helloworld example shouldn't be there. We are using a custom copy of the helloworld.proto here, which arguably, we should not.)
• I removed the need for a envoy.Dockerfile. We can just run the standard Envoy image and pass in our custom envoy.yaml.