Prune special labels from root project

These labels should never apply to the root project, but submit_filter
only applies to child projects. Add a submit_rule that only applies
to this root project so that commits are not blocked by the special
labels.

Change-Id: I3b7fda06667e277f56f0f63ef87a14c3dab38b66
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/+/1802316
diff --git a/rules.pl b/rules.pl
index 845a045..951391c 100644
--- a/rules.pl
+++ b/rules.pl
@@ -14,6 +14,13 @@
     Temp =.. [submit | C],
     check_find_owners(Temp, Out).
 
+% Prune the special labels from commits applying to this root project repository.
+submit_rule(X) :-
+    X =.. [submit | A],
+    check_branch_review(A, B),
+    check_bot_commit(B, C),
+    gerrit:default_submit(C).
+
 %% opt_in_find_owners
 %  Governs which changes are affected by the find-owners submit filter.
 %  Please keep clauses restricted to single projects, users, branches, or