Revert "Add global checkpoint assertion in index shard"

This reverts commit 89b305c.

Author: jasontedor

core/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -1515,8 +1515,6 @@ public long getGlobalCheckpoint() {
      */
     public void updateGlobalCheckpointOnReplica(final long globalCheckpoint) {
         verifyReplicationTarget();
-        // we sample the recovery stage before sampling the local checkpoint or we are subject to a race condition in the below assertion
-        final RecoveryState.Stage stage = recoveryState().getStage();
         final SequenceNumbersService seqNoService = getEngine().seqNoService();
         final long localCheckpoint = seqNoService.getLocalCheckpoint();
         if (globalCheckpoint > localCheckpoint) {
@@ -1526,10 +1524,10 @@ public void updateGlobalCheckpointOnReplica(final long globalCheckpoint) {
              * case that the global checkpoint update from the primary is ahead of the local checkpoint on this shard. In this case, we
              * ignore the global checkpoint update. This can happen if we are in the translog stage of recovery. Prior to this, the engine
              * is not opened and this shard will not receive global checkpoint updates, and after this the shard will be contributing to
-             * calculations of the the global checkpoint.
+             * calculations of the the global checkpoint. However, we can not assert that we are in the translog stage of recovery here as
+             * while the global checkpoint update may have emanated from the primary when we were in that state, we could subsequently move
+             * to recovery finalization, or even finished recovery before the update arrives here.
              */
-            assert stage == RecoveryState.Stage.TRANSLOG
-                    : "expected recovery stage [" + RecoveryState.Stage.TRANSLOG + "] but was [" + stage + "]";
             return;
         }
         seqNoService.updateGlobalCheckpointOnReplica(globalCheckpoint);