Remove unused backend service (sourcegraph#4050)

* Remove unused backend service

* Remove reference to deleted file

Author: caugustus-sourcegraph

base/backend.Service.yaml

@@ -4,7 +4,6 @@ resources:
 - base/cadvisor/cadvisor.DaemonSet.yaml
 - base/searcher/searcher.Service.yaml
 - base/searcher/searcher.Deployment.yaml
-- base/backend.Service.yaml
 - base/frontend/sourcegraph-frontend-internal.Service.yaml
 - base/frontend/sourcegraph-frontend.Deployment.yaml
 - base/frontend/sourcegraph-frontend.ServiceAccount.yaml