test: remove external CIs

CirrusCI and AppVeyor are great for automated tests and builds,
and they offer service for free for open source stuff which is
amazing and much appreciated.

Unfortunately it takes time to keep setup up-to-date when bumping
dependencies and/or nodejs version, so at least for now, only GitHub's
built-in actions will be used.

README.md

@@ -7,9 +7,9 @@ It creates CRXv3 files, which work for Chrome versions 64.0.3242 and above.
 
 If you need to create web extension file for older browser versions, where CRXv3 is not supported, use [CRX module](https://github.com/oncletom/crx) instead.
 
-It requires Node.js version 12 (or above) and runs on Linux, MacOS and Windows.
+It requires Node.js version 22 (or above) and runs on Linux, MacOS and Windows.
 
-> [![Build status on Linux & MacOS](https://api.cirrus-ci.com/github/ahwayakchih/crx3.svg?branch=master)](https://cirrus-ci.com/github/ahwayakchih/crx3/master "Linux & MacOS build logs") [![Build status on Windows](https://ci.appveyor.com/api/projects/status/oylw6nx8ebj5rw1e/branch/master?svg=true)](https://ci.appveyor.com/project/ahwayakchih/crx3/branch/master "Windows build log") [![Build status on Linux, MacOS and Windows](https://github.com/ahwayakchih/crx3/actions/workflows/test.yml/badge.svg?branch=master)](https://github.com/ahwayakchih/crx3/actions/workflows/test.yml "Linux, MacOS and Windows build logs")
+[![Build status on Linux, MacOS and Windows](https://github.com/ahwayakchih/crx3/actions/workflows/test.yml/badge.svg?branch=master)](https://github.com/ahwayakchih/crx3/actions/workflows/test.yml "Linux, MacOS and Windows build logs")
 
 # Installation