Remove duplicate libcore failures expectations.

Some jsr166 entries were already listed in
libcore/expectations/knownfailures.txt.

Bug: 28977632
Change-Id: I35788008262bac6f10d96f53e8e8f21e2364f091
diff --git a/tools/libcore_failures.txt b/tools/libcore_failures.txt
index 38b6ea6..bd5ff18 100644
--- a/tools/libcore_failures.txt
+++ b/tools/libcore_failures.txt
@@ -288,12 +288,5 @@
   description: "Only work with --mode=activity",
   result: EXEC_FAILED,
   names: [ "libcore.java.io.FileTest#testJavaIoTmpdirMutable" ]
-},
-{
-  description: "Made for extending, shouldn't be run",
-  result: EXEC_FAILED,
-  names: ["jsr166.CollectionTest#testEmptyMeansEmpty",
-          "jsr166.Collection8Test#testForEach",
-          "jsr166.Collection8Test#testForEachConcurrentStressTest"]
 }
 ]