chore: Remove coverage badge (#1811)

It's currently showing 0% eventhough the actual coverage is 58%.
Furthermore, the number doesn't really reflect the quality of the
codebase because it's not smart enough to exclude non-critical and
untestable code such as test helpers and command line setup code.

Signed-off-by: Charith Ellawala <charith@cerbos.dev>

README.md

@@ -1,4 +1,4 @@
-![GitHub release (latest SemVer)](https://img.shields.io/github/v/release/cerbos/cerbos?color=green&logo=github&sort=semver)  [![Snapshots](https://github.com/cerbos/cerbos/actions/workflows/snapshot.yaml/badge.svg)](https://github.com/cerbos/cerbos/actions/workflows/snapshot.yaml)  [![Go Reference](https://pkg.go.dev/badge/github.com/cerbos/cerbos/client.svg)](https://pkg.go.dev/github.com/cerbos/cerbos/client)   [![Go Report Card](https://goreportcard.com/badge/github.com/cerbos/cerbos)](https://goreportcard.com/report/github.com/cerbos/cerbos)  [![Coverage Status](https://coveralls.io/repos/github/cerbos/cerbos/badge.svg?branch=main)](https://coveralls.io/github/cerbos/cerbos?branch=main)  [![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.0-4baaaa.svg)](CODE_OF_CONDUCT.md)
+![GitHub release (latest SemVer)](https://img.shields.io/github/v/release/cerbos/cerbos?color=green&logo=github&sort=semver)  [![Snapshots](https://github.com/cerbos/cerbos/actions/workflows/snapshot.yaml/badge.svg)](https://github.com/cerbos/cerbos/actions/workflows/snapshot.yaml)  [![Go Reference](https://pkg.go.dev/badge/github.com/cerbos/cerbos/client.svg)](https://pkg.go.dev/github.com/cerbos/cerbos/client)   [![Go Report Card](https://goreportcard.com/badge/github.com/cerbos/cerbos)](https://goreportcard.com/report/github.com/cerbos/cerbos)  [![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.0-4baaaa.svg)](CODE_OF_CONDUCT.md)
 
 <p align="center">
   <img src="https://github.com/cerbos/cerbos/blob/main/docs/supplemental-ui/logo.png?raw=true" alt="Cerbos"/>