README.md: remove broken Build status (#44)

The Build status is broken for while, and we remove it as it is annoying to watch.

README.md

@@ -1,7 +1,6 @@
 # `aiida-phonopy`
 [![pre-commit](https://img.shields.io/badge/pre--commit-enabled-brightgreen?logo=pre-commit&logoColor=white)](https://github.com/pre-commit/pre-commit)
 [![PyPI version](https://badge.fury.io/py/aiida-phonopy.svg)](https://badge.fury.io/py/aiida-phonopy)
-[![Build Status](https://github.com/aiida-phonopy/aiida-phonopy/workflows/aiida-phonopy/badge.svg?branch=develop&event=push)](https://github.com/aiida-phonopy/aiida-phonopy/actions)
 [![Docs status](https://readthedocs.org/projects/aiida-phonopy/badge)](http://aiida-phonopy.readthedocs.io/)
 
 This is the official AiiDA plugin for [Phonopy](https://phonopy.github.io/phonopy/index.html).