Revert "Fix checkpoint handling to prevent segment replication infinite loop (opensearch-project#18636)"

This reverts commit 46a0045.

Author: andrross

server/src/main/java/org/opensearch/indices/replication/SegmentReplicationTargetService.java

@@ -50,7 +50,6 @@
 
 import java.io.IOException;
 import java.util.List;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -350,10 +349,7 @@ public void onReplicationDone(SegmentReplicationState state) {
 
                         // if we received a checkpoint during the copy event that is ahead of this
                         // try and process it.
-                        ReplicationCheckpoint latestReceivedCheckpoint = replicator.getPrimaryCheckpoint(replicaShard.shardId());
-                        if (Objects.nonNull(latestReceivedCheckpoint) && latestReceivedCheckpoint.isAheadOf(receivedCheckpoint)) {
-                            processLatestReceivedCheckpoint(replicaShard, thread);
-                        }
+                        processLatestReceivedCheckpoint(replicaShard, thread);
                     }
 
                     @Override

server/src/test/java/org/opensearch/indices/replication/SegmentReplicationTargetServiceTests.java

@@ -637,7 +637,6 @@ public void testStartReplicationListenerSuccess() throws InterruptedException {
 
         latch.await(2, TimeUnit.SECONDS);
         verify(spy, (atLeastOnce())).updateVisibleCheckpoint(eq(0L), eq(replicaShard));
-        verify(spy, times(1)).processLatestReceivedCheckpoint(any(), any());
     }
 
     public void testStartReplicationListenerFailure() throws InterruptedException {