Remove non-functional CI

After 9 years the following services no longer work for
this repository:

- Travis CI
- Appveyor
- Coveralls.io

Presumably all services have changed their terms of
services in this time. I have no interest in figuring
out why for such a simple package.

README.md

@@ -2,10 +2,7 @@
 ## strip UTF-8 byte order marks
 
 [![GoDoc](https://pkg.go.dev/badge/github.com/spkg/bom)](https://godoc.org/github.com/spkg/bom)
-[![Build Status (Linux)](https://travis-ci.org/spkg/bom.svg?branch=master)](https://travis-ci.org/spkg/bom)
-[![Build status (Windows)](https://ci.appveyor.com/api/projects/status/065x7yuc77xicv59?svg=true)](https://ci.appveyor.com/project/jjeffery/bom)
 [![License](http://img.shields.io/badge/license-MIT-green.svg?style=flat)](https://raw.githubusercontent.com/spkg/bom/master/LICENSE.md)
-[![Coverage Status](https://coveralls.io/repos/github/spkg/bom/badge.svg?branch=master)](https://coveralls.io/github/spkg/bom?branch=master)
 [![GoReportCard](https://goreportcard.com/badge/github.com/spkg/bom)](http://goreportcard.com/report/spkg/bom)