github: simplify CODEOWNERS
-.github/ @concourse/maintainers
+* @concourse/maintainers
CODE_OF_CONDUCT.md @concourse/community
-CONTRIBUTING.md @concourse/maintainers
-web/ @concourse/maintainers
-package.json @concourse/maintainers
-yarn.lock @concourse/maintainers
-fly/ @concourse/maintainers
-go-concourse/ @concourse/maintainers
-atc/ @concourse/maintainers
-skymarshal/ @concourse/maintainers
-vars/ @concourse/maintainers
-atc/exec/ @concourse/maintainers
-atc/worker/ @concourse/maintainers
-atc/runtime/ @concourse/maintainers
-worker/ @concourse/maintainers
-tsa/ @concourse/maintainers
