Remove older devtools hook

Summary:
As of v1.4.0, a new devtools hook is used that is hosted within `relay-devtools` instead of `relay-runtime`. That allows debugging of production relay apps, and reduces byte size of Relay.

As a result, relay-debugger-react-native-runtime and RelayDebugger can be removed.

Reviewed By: kassens

Differential Revision: D5904296

fbshipit-source-id: 2b215f5a25ecb2922b00cdf86f7d31415d8d1328

Libraries/Core/Devtools/setupDevtools.js

@@ -34,7 +34,6 @@ if (__DEV__) {
    * comment and run Flow. */
   const reactDevTools = require('react-devtools-core');
 
-  register = function (plugin: DevToolsPlugin) {
   // Initialize dev tools only if the native module for WebSocket is available
   if (WebSocket.isAvailable) {
     // Don't steal the DevTools from currently active app.
@@ -48,7 +47,7 @@ if (__DEV__) {
       PlatformConstants.ServerHost.split(':')[0] :
       'localhost';
 
-      plugin.connectToDevTools({
+    reactDevTools.connectToDevTools({
       isAppActive,
       host,
       // Read the optional global variable for backward compatibility.
@@ -57,10 +56,6 @@ if (__DEV__) {
       resolveRNStyle: require('flattenStyle'),
     });
   }
-  };
-
-  register(reactDevTools);
-  global.registerDevtoolsPlugin = register;
 }
 
 module.exports = {