ci: drop AppVeyor and its badge

Author: ahlinc

.appveyor.yml

@@ -1,7 +1,6 @@
 # tree-sitter
 
 [![Build Status](https://github.com/tree-sitter/tree-sitter/workflows/CI/badge.svg)](https://github.com/tree-sitter/tree-sitter/actions)
-[![Build status](https://ci.appveyor.com/api/projects/status/vtmbd6i92e97l55w/branch/master?svg=true)](https://ci.appveyor.com/project/maxbrunsfeld/tree-sitter/branch/master)
 [![DOI](https://zenodo.org/badge/14164618.svg)](https://zenodo.org/badge/latestdoi/14164618)
 
 Tree-sitter is a parser generator tool and an incremental parsing library. It can build a concrete syntax tree for a source file and efficiently update the syntax tree as the source file is edited. Tree-sitter aims to be: