coverage: Remove sonar coverage setup (#13000)

Looks like this never was really enabled properly and it's not working
at the moment. We never run these jobs on branches and the badge for
sonarcloud is broken as well.

Let's remove this for now. If we want coverage back, we need to redo it
anyway and newer Go releases like Go 1.20 have better support for doing
coverage anyway so we'd need to do it differently regardless.

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>

README.md

@@ -1,10 +1,8 @@
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/io.vitess/vitess-jdbc/badge.svg)](https://maven-badges.herokuapp.com/maven-central/io.vitess/vitess-jdbc)
-[![Build Status](https://travis-ci.org/vitessio/vitess.svg?branch=master)](https://travis-ci.org/vitessio/vitess/builds)
 [![codebeat badge](https://codebeat.co/badges/51c9a056-1103-4522-9a9c-dc623821ea87)](https://codebeat.co/projects/github-com-youtube-vitess)
 [![Go Report Card](https://goreportcard.com/badge/vitess.io/vitess)](https://goreportcard.com/report/vitess.io/vitess)
 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bgithub.com%2Fvitessio%2Fvitess.svg?type=shield)](https://app.fossa.io/projects/git%2Bgithub.com%2Fvitessio%2Fvitess?ref=badge_shield)
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1724/badge)](https://bestpractices.coreinfrastructure.org/projects/1724)
-[![Coverage](https://sonarcloud.io/api/project_badges/measure?project=vitessio&metric=coverage)](https://sonarcloud.io/dashboard?id=vitessio)
 
 # Vitess