Remove issue stats from README.md, as they don't ever update

fixes https://github.com/Microsoft/visualfsharp/issues/165

README.md

-[![Issue Stats](http://issuestats.com/github/Microsoft/visualfsharp/badge/pr)](http://issuestats.com/github/microsoft/visualfsharp)
-[![Issue Stats](http://issuestats.com/github/Microsoft/visualfsharp/badge/issue)](http://issuestats.com/github/microsoft/visualfsharp)
 [![Build status](https://img.shields.io/appveyor/ci/KevinRansom/visualfsharp-radou/fsharp4.svg)](https://ci.appveyor.com/project/KevinRansom/visualfsharp-radou/branch/fsharp4)
 
 [![Join the chat at https://gitter.im/Microsoft/visualfsharp](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/Microsoft/visualfsharp?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)