Kafka: Fixes needlessly low interpretation of maxRowsInMemory. (#5034)

AppenderatorImpl already applies maxRowsInMemory across all sinks. So dividing by
the number of Kafka partitions is pointless and effectively makes the interpretation
of maxRowsInMemory lower than expected.

This undoes one of the two changes from #3284, which fixed the original bug twice.
In this, that's worse than fixing it once.

extensions-core/kafka-indexing-service/src/main/java/io/druid/indexing/kafka/KafkaIndexTask.java

@@ -957,12 +957,9 @@ public class KafkaIndexTask extends AbstractTask implements ChatHandler
 
   private Appenderator newAppenderator(FireDepartmentMetrics metrics, TaskToolbox toolbox)
   {
-    final int maxRowsInMemoryPerPartition = (tuningConfig.getMaxRowsInMemory() /
-                                             ioConfig.getStartPartitions().getPartitionOffsetMap().size());
     return Appenderators.createRealtime(
         dataSchema,
-        tuningConfig.withBasePersistDirectory(toolbox.getPersistDir())
-                    .withMaxRowsInMemory(maxRowsInMemoryPerPartition),
+        tuningConfig.withBasePersistDirectory(toolbox.getPersistDir()),
         metrics,
         toolbox.getSegmentPusher(),
         toolbox.getObjectMapper(),

extensions-core/kafka-indexing-service/src/main/java/io/druid/indexing/kafka/KafkaTuningConfig.java

@@ -185,22 +185,6 @@ public class KafkaTuningConfig implements TuningConfig, AppenderatorConfig
     );
   }
 
-  public KafkaTuningConfig withMaxRowsInMemory(int rows)
-  {
-    return new KafkaTuningConfig(
-        rows,
-        maxRowsPerSegment,
-        intermediatePersistPeriod,
-        basePersistDirectory,
-        maxPendingPersists,
-        indexSpec,
-        true,
-        reportParseExceptions,
-        handoffConditionTimeout,
-        resetOffsetAutomatically
-    );
-  }
-
   @Override
   public boolean equals(Object o)
   {