Remove unnecessary BwC in StatelessPrimaryRelocationAction (elastic#1…

…05538)

There are no remaining clusters using this action with the pre-8.11.x
transport protocol so we can remove the BwC here.

server/src/main/java/org/elasticsearch/indices/recovery/StatelessPrimaryRelocationAction.java

@@ -8,7 +8,6 @@
 
 package org.elasticsearch.indices.recovery;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequest;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.ActionResponse;
@@ -49,11 +48,7 @@ public Request(StreamInput in) throws IOException {
             shardId = new ShardId(in);
             targetNode = new DiscoveryNode(in);
             targetAllocationId = in.readString();
-            if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_11_X)) {
-                clusterStateVersion = in.readVLong();
-            } else {
-                clusterStateVersion = 0L; // temporary bwc: do not wait for cluster state to be applied
-            }
+            clusterStateVersion = in.readVLong();
         }
 
         @Override
@@ -68,9 +63,7 @@ public void writeTo(StreamOutput out) throws IOException {
             shardId.writeTo(out);
             targetNode.writeTo(out);
             out.writeString(targetAllocationId);
-            if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_11_X)) {
-                out.writeVLong(clusterStateVersion);
-            } // temporary bwc: just omit it, the receiver doesn't wait for a cluster state anyway
+            out.writeVLong(clusterStateVersion);
         }
 
         public long recoveryId() {