Remove some dead aggs code around delayed aggs (#119620)

Looks like the removed classes never went anywhere => we should remove the dead code for the time being.

Author: original-brownbear

server/src/main/java/org/elasticsearch/search/aggregations/bucket/BucketsAggregator.java

@@ -59,13 +59,6 @@ public BucketsAggregator(
         docCountProvider = new DocCountProvider();
     }
 
-    /**
-     * Return an upper bound of the maximum bucket ordinal seen so far.
-     */
-    public final long maxBucketOrd() {
-        return docCounts.size();
-    }
-
     /**
      * Ensure there are at least <code>maxBucketOrd</code> buckets available.
      */

server/src/main/java/org/elasticsearch/search/aggregations/bucket/DelayedBucketReducer.java

@@ -271,13 +271,6 @@ public InternalAggregation finalizeSampling(SamplingContext samplingContext) {
         );
     }
 
-    private Bucket reduceBucket(List<Bucket> buckets, AggregationReduceContext context) {
-        assert buckets.isEmpty() == false;
-        final List<InternalAggregations> aggregations = new BucketAggregationList<>(buckets);
-        final InternalAggregations aggs = InternalAggregations.reduce(aggregations, context);
-        return createBucket(aggs, buckets.get(0));
-    }
-
     @Override
     public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         if (keyed) {