eclass-overlay: Remove chronos from ml-service gid

It isn't needed.

TEST=Exercised ML Service with a locally modified Chrome.
BUG=chromium:863780

Change-Id: I7e31b988664b077bf3fa221c068b1a34d799ab1c
Reviewed-on: https://chromium-review.googlesource.com/1239819
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Andrew Moylan <amoylan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/profiles/base/accounts/group/ml-service b/profiles/base/accounts/group/ml-service
index e5eaf7e..925f09e 100644
--- a/profiles/base/accounts/group/ml-service
+++ b/profiles/base/accounts/group/ml-service
@@ -1,3 +1,3 @@
 group:ml-service
 gid:20106
-users:chronos,ml-service
+users:ml-service