Remove window shim from ExecJS render

This can cause issues when using 3rd party libraries that do a presence
check on window to determine if browser functions are available

Author: Nick Maher

lib/react/server_rendering/exec_js_renderer.rb

@@ -33,7 +33,6 @@ def after_render(component_name, props, prerender_options); ""; end
       GLOBAL_WRAPPER = <<-JS
         var global = global || this;
         var self = self || this;
-        var window = window || this;
       JS
 
     end