Remove TopNBlockHash abstract class

Author: ivancea

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/aggregation/blockhash/LongTopNBlockHash.java

@@ -31,7 +31,7 @@
  * Maps a {@link LongBlock} column to group ids, keeping only the top N values.
  */
 // TODO: package-private instead of public?
-public final class LongTopNBlockHash extends TopNBlockHash {
+public final class LongTopNBlockHash extends BlockHash {
     private final int channel;
     private final boolean asc;
     private final boolean nullsFirst;