Remove extra Continuous Integration files; move towards GitHub Actions

Author: valentinitnelav

.travis.yml

@@ -1,9 +1,5 @@
 # plotbiomes
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.7145245.svg)](https://doi.org/10.5281/zenodo.7145245)
-<!-- CI badges -->
-[![AppVeyor Build status](https://ci.appveyor.com/api/projects/status/jag1bo7jaao5jid3/branch/develop?svg=true)](https://ci.appveyor.com/project/valentinitnelav/plotbiomes/branch/develop)
-[![Travis Build Status](https://travis-ci.org/valentinitnelav/plotbiomes.svg?branch=develop)](https://travis-ci.org/valentinitnelav/plotbiomes)
-[![Coverage Status](https://img.shields.io/codecov/c/github/valentinitnelav/plotbiomes/master.svg)](https://codecov.io/github/valentinitnelav/plotbiomes?branch=master)
 
 <!--
 Fixing errors from Travis CI can be time consuming ...