remove HLL version specific code outside of HyperLogLogCollector

processing/src/main/java/io/druid/query/aggregation/hyperloglog/HLLCV0.java

@@ -37,12 +37,12 @@ public class HLLCV0 extends HyperLogLogCollector
 
   private static final ByteBuffer defaultStorageBuffer = ByteBuffer.wrap(new byte[]{0, 0, 0}).asReadOnlyBuffer();
 
-  public HLLCV0()
+  protected HLLCV0()
   {
     super(defaultStorageBuffer);
   }
 
-  public HLLCV0(ByteBuffer buffer)
+  protected HLLCV0(ByteBuffer buffer)
   {
     super(buffer);
   }
@@ -149,4 +149,4 @@ public class HLLCV0 extends HyperLogLogCollector
   {
     return buffer.position() + HEADER_NUM_BYTES;
   }
-}
+}

processing/src/main/java/io/druid/query/aggregation/hyperloglog/HLLCV1.java

@@ -44,12 +44,12 @@ public class HLLCV1 extends HyperLogLogCollector
   private static final ByteBuffer defaultStorageBuffer = ByteBuffer.wrap(new byte[]{VERSION, 0, 0, 0, 0, 0, 0})
                                                                    .asReadOnlyBuffer();
 
-  public HLLCV1()
+  protected HLLCV1()
   {
     super(defaultStorageBuffer);
   }
 
-  public HLLCV1(ByteBuffer buffer)
+  protected HLLCV1(ByteBuffer buffer)
   {
     super(buffer);
   }

processing/src/main/java/io/druid/query/aggregation/hyperloglog/HyperUniquesSerde.java

@@ -121,9 +121,7 @@ public class HyperUniquesSerde extends ComplexMetricSerde
       public HyperLogLogCollector fromByteBuffer(ByteBuffer buffer, int numBytes)
       {
         buffer.limit(buffer.position() + numBytes);
-
-        int remaining = buffer.remaining();
-        return (remaining % 3 == 0 || remaining == 1027) ? new HLLCV0(buffer) : new HLLCV1(buffer);
+        return HyperLogLogCollector.makeCollector(buffer);
       }
 
       @Override