[docs] Remove badge which points out that the project uses Black as a code formatter.

This information is not relevant for users.

Signed-off-by: Michael Seifert <m.seifert@digitalernachschub.de>

Author: seifertm

README.rst

@@ -10,8 +10,6 @@ pytest-asyncio
 .. image:: https://img.shields.io/pypi/pyversions/pytest-asyncio.svg
     :target: https://github.com/pytest-dev/pytest-asyncio
     :alt: Supported Python versions
-.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
-    :target: https://github.com/ambv/black
 .. image:: https://img.shields.io/badge/Matrix-%23pytest--asyncio-brightgreen
     :alt: Matrix chat room: #pytest-asyncio
     :target: https://matrix.to/#/#pytest-asyncio:matrix.org