ART buildbots: Stop blacklisting SystemTest#testArrayCopyConcurrentModification

The test was blacklisted ages ago but it's not clear whether it
still fails. As requested in http://b/19165288#comment22 ,
this CL removes the test from the blacklist so that we can get
data on whether it still occassionally fails.

Bug: 19165288
Test: Treehugger only, didn't run the test.
Change-Id: I0404a997956dfe757adfa6fb30c8c22e038bb900
diff --git a/tools/libcore_failures.txt b/tools/libcore_failures.txt
index 157eed1..9a68779 100644
--- a/tools/libcore_failures.txt
+++ b/tools/libcore_failures.txt
@@ -105,12 +105,6 @@
   names: ["org.apache.harmony.tests.java.lang.ProcessTest#test_getErrorStream"]
 },
 {
-  description: "Test sometimes timeouts on volantis, and on most modes in debug mode",
-  result: EXEC_TIMEOUT,
-  names: ["libcore.java.lang.SystemTest#testArrayCopyConcurrentModification"],
-  bug: 19165288
-},
-{
   description: "Needs kernel updates on host/device",
   result: EXEC_FAILED,
   names: ["libcore.libcore.io.OsTest#test_socketPing"]