DOC: Remove CircleCI badge

Replaced by GitHub Actions.

Author: thewtex

README.rst

@@ -17,10 +17,6 @@ itkwidgets
     :target: https://github.com/InsightSoftwareConsortium/itkwidgets/actions?query=workflow%3A%22Build+and+test%22
     :alt: Build status
 
-.. image:: https://circleci.com/gh/InsightSoftwareConsortium/itkwidgets.svg?style=shield
-    :target: https://circleci.com/gh/InsightSoftwareConsortium/itkwidgets
-    :alt: Build status
-
 .. image:: https://mybinder.org/badge_logo.svg
     :target: https://mybinder.org/v2/gh/InsightSoftwareConsortium/itkwidgets/master?urlpath=lab/tree/examples%2F3DImage.ipynb
     :alt: Interactive example on MyBinder