test: remove comment about new head warning
The new head warning was buggy. This was fixed in bdc5bb223b50.
--- a/tests/test-topic-stack.t Sun Apr 03 21:41:38 2016 -0700
+++ b/tests/test-topic-stack.t Mon Apr 04 00:17:54 2016 -0700
@@ -10,7 +10,6 @@
> evolution=createmarkers,exchange,allowunstable
> EOF
-(new head warning seems buggy)
$ hg init main
$ cd main
$ echo aaa > aaa