Revert source graph branch (#1210)

I think this badge is misleading as we are not a library so the number of projects we are used in is not really relevant to our adoption. It is more-or-less just the number of external plugins people have built.

README.md

@@ -6,7 +6,6 @@
 [![Go Report Card](https://goreportcard.com/badge/github.com/coredns/coredns)](https://goreportcard.com/report/coredns/coredns)
 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Fcoredns%2Fcoredns.svg?type=shield)](https://app.fossa.io/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Fcoredns%2Fcoredns?ref=badge_shield)
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1250/badge)](https://bestpractices.coreinfrastructure.org/projects/1250)
-[![Sourcegraph](https://sourcegraph.com/github.com/coredns/coredns/-/badge.svg)](https://sourcegraph.com/github.com/coredns/coredns?badge)
 
 CoreDNS (written in Go) chains [plugins](https://coredns.io/plugins). Each plugin performs a DNS
 function.