Updating telemeter builder & base images to be consistent with ART

Reconciling with https://github.com/openshift/ocp-build-data/tree/4a98c8d67fb1b0233d689c4bcc7f97e61da53999/images/telemeter.yml

Dockerfile

@@ -1,12 +1,12 @@
-FROM registry.svc.ci.openshift.org/ocp/builder:rhel-8-golang-1.15-openshift-4.6
+FROM registry.ci.openshift.org/ocp/builder:rhel-8-golang-1.15-openshift-4.6
 ENV GOFLAGS="-mod=vendor"
 COPY . /go/src/github.com/openshift/telemeter
 RUN cd /go/src/github.com/openshift/telemeter && \
     go build ./cmd/telemeter-client && \
     go build ./cmd/telemeter-server && \
     go build ./cmd/authorization-server
 
-FROM registry.svc.ci.openshift.org/ocp/4.6:base
+FROM registry.ci.openshift.org/ocp/4.6:base
 LABEL io.k8s.display-name="OpenShift Telemeter" \
       io.k8s.description="" \
       io.openshift.tags="openshift,monitoring" \