Remove empty instanceManager file

Remove the empty/incomplete instanceManager implementation.

lib/manager/instanceManager.js

@@ -1,2 +0,0 @@
-const fs = require("fs-extra");
-const needle = require("needle");

test/missing.js

@@ -1,7 +1,6 @@
 // These are libraries that does not have any units test, they are
 // required here in order to track coverage for them.
 
-require('lib/manager/instanceManager');
 require('lib/manager/modManager');
 require('lib/manager/pluginManager');
 require('lib/npmPostinstall.js');