Update test case

Author: nmayorsplit

client/src/test/java/io/split/client/impressions/UniqueKeysTrackerImpTest.java

@@ -95,8 +95,6 @@ public void testStopSynchronization() throws Exception {
         Assert.assertTrue(uniqueKeysTrackerImp.track("feature1","key2"));
         Assert.assertTrue(uniqueKeysTrackerImp.track("feature2","key3"));
 
-        Thread.sleep(1000);
-        Assert.assertTrue(uniqueKeysTrackerImp.getSendGuard().get());
         Thread.sleep(2100);
         Mockito.verify(telemetrySynchronizer, Mockito.times(1)).synchronizeUniqueKeys(Mockito.anyObject());
         uniqueKeysTrackerImp.stop();