Remove {Indices,}ClusterStateUpdateRequest (elastic#113483) (elastic#113506)

These abstract classes are now unused so this commit removes them.

Author: DaveCTurner

server/src/main/java/module-info.java

@@ -160,7 +160,6 @@
     exports org.elasticsearch.client.internal.support;
     exports org.elasticsearch.client.internal.transport;
     exports org.elasticsearch.cluster;
-    exports org.elasticsearch.cluster.ack;
     exports org.elasticsearch.cluster.action.index;
     exports org.elasticsearch.cluster.action.shard;
     exports org.elasticsearch.cluster.block;