[CI] Change metrics container to upstream version

Now that infrastructure has landed in the monorepo for the metrics container
and we have a workflow to build the container and push it to the LLVM GCR,
switch to using that container definition rather than the one in our
downstream fork.

Author: boomanaiden154

premerge/metrics_deployment.yaml

@@ -17,9 +17,7 @@ spec:
     spec:
       containers:
       - name: metrics
-        # TODO(boomanaiden154): Update this image when we have the metrics
-        # container build job in the monorepo.
-        image: ghcr.io/keenuts-test-org/llvm-premerge-infra-metrics:debug
+        image: ghcr.io/llvm/metrics:latest
         env:
         - name: GITHUB_TOKEN
           valueFrom: