Always set `publish_binary` to empty for generated rbe platforms (#2023)

diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index e10dd82..f91223b 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -550,6 +550,7 @@
         rbe_platform_dict = copy.deepcopy(platform_dict)
         rbe_platform_dict["name"] = "RBE {}".format(platform_dict["name"])
         rbe_platform_dict["emoji-name"] = "RBE {}".format(platform_dict["emoji-name"])
+        rbe_platform_dict["publish_binary"] = []
         PLATFORMS["rbe_{}".format(platform)] = rbe_platform_dict
 
 BUILDIFIER_DOCKER_IMAGE = "gcr.io/bazel-public/buildifier"