Unify and fix checkers for duplicate object literal properties.

test/preparser/preparser.status

Index: test/preparser/preparser.status
diff --git a/test/preparser/preparser.status b/test/preparser/preparser.status
index 37512bdeedacbd940a7d7bbdd4f861b74a41d35c..9d69988f71f561da18fd92198092587e7380c38a 100644
--- a/test/preparser/preparser.status
+++ b/test/preparser/preparser.status
@@ -27,12 +27,6 @@
 
 [
 [ALWAYS, {
-  # TODO(mstarzinger): Uhm, this is kind of embarrassing, but our parser
-  # does not catch some syntax errors with duplicate properties in object
-  # literals that our preparser actually caught. I will fix this glitch in a
-  # follow-up change.
-  'duplicate-property/*': [SKIP],
-
   # TODO(mstarzinger): This script parses but throws a TypeError when run.
   'non-alphanum': [FAIL],