Remove deprecated constant META_FIELDS_BEFORE_7DOT8 (opensearch-project#13860)

* Add _primary_term to builtInMetadataMappers

Signed-off-by: Craig Perkins <cwperx@amazon.com>

* Add to CHANGELOG

Signed-off-by: Craig Perkins <cwperx@amazon.com>

* Remove deprecated constant META_FIELDS_BEFORE_7DOT8

Signed-off-by: Craig Perkins <cwperx@amazon.com>

* Update CHANGELOG

Signed-off-by: Craig Perkins <cwperx@amazon.com>

---------

Signed-off-by: Craig Perkins <cwperx@amazon.com>

Author: cwperks

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - [Remote Store] Upload translog checkpoint as object metadata to translog.tlog([#13637](https://github.com/opensearch-project/OpenSearch/pull/13637))
 - Add getMetadataFields to MapperService ([#13819](https://github.com/opensearch-project/OpenSearch/pull/13819))
 - [Remote State] Add async remote state deletion task running on an interval, configurable by a setting ([#13131](https://github.com/opensearch-project/OpenSearch/pull/13131))
+- Remove deprecated constant META_FIELDS_BEFORE_7DOT8 ([#13860](https://github.com/opensearch-project/OpenSearch/pull/13860))
 
 ### Dependencies
 - Bump `com.github.spullara.mustache.java:compiler` from 0.9.10 to 0.9.13 ([#13329](https://github.com/opensearch-project/OpenSearch/pull/13329), [#13559](https://github.com/opensearch-project/OpenSearch/pull/13559))

server/src/main/java/org/opensearch/index/mapper/MapperService.java

@@ -73,7 +73,6 @@
 import java.io.Closeable;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -201,11 +200,6 @@ public enum MergeReason {
         Property.IndexScope,
         Property.Deprecated
     );
-    // Deprecated set of meta-fields, for checking if a field is meta, use an instance method isMetadataField instead
-    @Deprecated
-    public static final Set<String> META_FIELDS_BEFORE_7DOT8 = Collections.unmodifiableSet(
-        new HashSet<>(Arrays.asList("_id", IgnoredFieldMapper.NAME, "_index", "_routing", "_size", "_timestamp", "_ttl", "_type"))
-    );
 
     private static final DeprecationLogger deprecationLogger = DeprecationLogger.getLogger(MapperService.class);