Delete Step_0.md

Remove separate step now everything's been moved into the main doc

Step_0.md

-# Step-0: define a service
-
-This section presents an example of a simple service definition that receives
-a message from a remote client. The message contains the user's name and
-sends back a greeting to that person.
-
-It's shown below in full; it's actually contained in separate file.
-[helloworld.proto](src/main/proto/helloworld.proto).
-
-```
-syntax = "proto3";
-
-package helloworld;
-
-// The request message containing the user's name.
-message HelloRequest {
-  optional string name = 1;
-}
-
-// The response message containing the greetings
-message HelloReply {
-  optional string message = 1;
-}
-
-// The greeting service definition.
-service Greeting {
-
-  // Sends a greeting
-  rpc hello (HelloRequest) returns (HelloReply) {
-  }
-}
-
-```
-
-The service stanza of the message is an example of protobuf service IDL
-(Interface Definition Language). Here, it defines a simple service that
-receives a request containing a name and returns a response containing a
-message.
-
-Next, in [Step - 1](Step_1.md), we'll use protoc to generate client code from
-this IDL.