Remove AppVeyor in favor of GH Actions Win build

Author: evgenyz

README.md

@@ -1,7 +1,6 @@
 # OpenSCAP
 
 [![Gating](https://github.com/OpenSCAP/openscap/actions/workflows/build.yml/badge.svg?branch=maint-1.3)](https://github.com/OpenSCAP/openscap/actions/workflows/build.yml)
-[![Build status](https://ci.appveyor.com/api/projects/status/3o5fnld1m98bo0so/branch/maint-1.3?svg=true)](https://ci.appveyor.com/project/OpenSCAP/openscap)
 [![Join the chat at https://gitter.im/OpenSCAP/openscap](https://badges.gitter.im/OpenSCAP/openscap.svg)](https://gitter.im/OpenSCAP/openscap?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 Open Source Security Compliance Solution