Revert "upgrade xstream to 1.4.20 to pick up fixes for 2 CVEs (apache…

…#2763)"

This reverts commit 53b5889.

This dependency is banned at li.

helix-core/src/test/java/org/apache/helix/integration/rebalancer/TestInstanceOperation.java

@@ -1258,8 +1258,6 @@ public void testMarkEvacuationAfterEMM() throws Exception {
       Assert.assertTrue(getParticipantsInEv(assignment.get(resource)).contains(instanceToEvacuate));
     }
 
-    Assert.assertTrue(_bestPossibleClusterVerifier.verifyByPolling());
-
     // exit MM
     _gSetupTool.getClusterManagementTool()
         .manuallyEnableMaintenanceMode(CLUSTER_NAME, false, null, null);