Stop publishing CentOS 7 binaries (#2286)

It has been EOL for almost a year now, and we have replaced it with
Rocky Linux 8.

Progress towards
#2272

Author: fweikert

buildkite/bazelci.py

@@ -269,7 +269,7 @@
     "centos7": {
         "name": "CentOS 7",
         "emoji-name": ":centos: CentOS 7",
-        "publish_binary": ["centos7"],
+        "publish_binary": [],
         "docker-image": f"gcr.io/{DOCKER_REGISTRY_PREFIX}/centos7",
         "python": "python3.6",
     },