Combine client testing documentation

Summary: There was one public page for testing client plugins, and two internal ones. Combined it into a one pager, that has tabs per target, with separate content for internal versus external (didn't combine those as the testing frameworks recommended differ)

Reviewed By: nikoant

Differential Revision: D25588058

fbshipit-source-id: afa151ec0c3a5de26142938d3d389627716f1ff7

website/sidebars.js

@@ -105,13 +105,11 @@ module.exports = {
         {
           Android: [
             'fb/android-plugin-development-Android-interacting-0',
-            'fb/android-plugin-development-testing-android-plugins-0',
           ],
         },
         {
           iOS: [
             'fb/ios-plugin-development-sending-data-to-an-ios-plugin-0',
-            'fb/ios-plugin-development-testing-ios-plugins-0',
           ],
         },
       ]),