Simplify Lucene60 and Luene62 codec constructors (elastic#124054) (elastic#124092)

The only public constructor needed in the archive index codecs is the default one,
as that's called by SPI. The other one will only ever be called by the default one,
hence we can merge the two into one and simplify things a bit.

Author: javanna

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene60/Lucene60Codec.java

@@ -38,8 +38,6 @@
 import org.elasticsearch.xpack.lucene.bwc.codecs.lucene50.Lucene50SegmentInfoFormat;
 import org.elasticsearch.xpack.lucene.bwc.codecs.lucene54.Lucene54DocValuesFormat;
 
-import java.util.Objects;
-
 /**
  * Implements the Lucene 6.0 index format.
  *
@@ -71,21 +69,12 @@ protected PostingsFormat getPostingsFormat(String formatName) {
     };
 
     /**
-     * Instantiates a new codec.
+     * Instantiates a new codec. Called by SPI.
      */
+    @SuppressWarnings("unused")
     public Lucene60Codec() {
-        this(Lucene50StoredFieldsFormat.Mode.BEST_SPEED);
-    }
-
-    /**
-     * Instantiates a new codec, specifying the stored fields compression
-     * mode to use.
-     * @param mode stored fields compression mode to use for newly
-     *             flushed/merged segments.
-     */
-    public Lucene60Codec(Lucene50StoredFieldsFormat.Mode mode) {
         super("Lucene60");
-        this.storedFieldsFormat = new Lucene50StoredFieldsFormat(Objects.requireNonNull(mode));
+        this.storedFieldsFormat = new Lucene50StoredFieldsFormat(Lucene50StoredFieldsFormat.Mode.BEST_SPEED);
     }
 
     @Override

x-pack/plugin/old-lucene-versions/src/main/java/org/elasticsearch/xpack/lucene/bwc/codecs/lucene62/Lucene62Codec.java

@@ -38,8 +38,6 @@
 import org.elasticsearch.xpack.lucene.bwc.codecs.lucene54.Lucene54DocValuesFormat;
 import org.elasticsearch.xpack.lucene.bwc.codecs.lucene60.Lucene60MetadataOnlyPointsFormat;
 
-import java.util.Objects;
-
 /**
  * Implements the Lucene 6.2 index format.
  *
@@ -70,13 +68,13 @@ protected PostingsFormat getPostingsFormat(String formatName) {
         }
     };
 
+    /**
+     * Instantiates a new codec. Called by SPI.
+     */
+    @SuppressWarnings("unused")
     public Lucene62Codec() {
-        this(Lucene50StoredFieldsFormat.Mode.BEST_SPEED);
-    }
-
-    public Lucene62Codec(Lucene50StoredFieldsFormat.Mode mode) {
         super("Lucene62");
-        this.storedFieldsFormat = new Lucene50StoredFieldsFormat(Objects.requireNonNull(mode));
+        this.storedFieldsFormat = new Lucene50StoredFieldsFormat(Lucene50StoredFieldsFormat.Mode.BEST_SPEED);
     }
 
     @Override