Remove redundant docs link (#2075)

The docs link doesn't work. I'm assuming that the intended thing is that people go to the turinglang.org page linked below the badges, meaning that this docs badge should be removed.

README.md

@@ -3,7 +3,6 @@
 [![Build Status](https://github.com/TuringLang/Turing.jl/workflows/Turing-CI/badge.svg)](https://github.com/TuringLang/Turing.jl/actions?query=workflow%3ATuring-CI+branch%3Amaster)
 [![Coverage Status](https://coveralls.io/repos/github/TuringLang/Turing.jl/badge.svg?branch=master)](https://coveralls.io/github/TuringLang/Turing.jl?branch=master)
 [![codecov](https://codecov.io/gh/TuringLang/Turing.jl/branch/master/graph/badge.svg?token=OiUBsnDQqf)](https://codecov.io/gh/TuringLang/Turing.jl)
-[![Documentation](https://img.shields.io/badge/doc-latest-blue.svg)](https://turinglang.org/dev/docs/using-turing/)
 [![ColPrac: Contributor's Guide on Collaborative Practices for Community Packages](https://img.shields.io/badge/ColPrac-Contributor's%20Guide-blueviolet)](https://github.com/SciML/ColPrac)