Fixed a comment on dirty logs list

We've recently changed default behaviour to forbid any dirty logs for
services outside the list instead of explicitly enabling log checks for
specific services. The comment was not updated to reflect the change
though.

Change-Id: I5d5ba64d156a9b5318cfc2740b2a69d75de3c127
diff --git a/tools/check_logs.py b/tools/check_logs.py
index 7cf9d85..c8d3a1a 100755
--- a/tools/check_logs.py
+++ b/tools/check_logs.py
@@ -31,7 +31,7 @@
 is_grenade = os.environ.get('DEVSTACK_GATE_GRENADE') is not None
 dump_all_errors = True
 
-# As logs are made clean, add to this set
+# As logs are made clean, remove from this set
 allowed_dirty = set([
     'c-api',
     'ceilometer-acentral',