Remove deprecated constant META_FIELDS_BEFORE_7DOT8 (#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>
(cherry picked from commit 9832972)

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Make outbound side of transport protocol dependent ([#13293](https://github.com/opensearch-project/OpenSearch/pull/13293))
 - [Remote Store] Upload translog checkpoint as object metadata to translog.tlog([#13637](https://github.com/opensearch-project/OpenSearch/pull/13637))
 - [Remote Store] Add dynamic cluster settings to set timeout for segments upload to Remote Store ([#13679](https://github.com/opensearch-project/OpenSearch/pull/13679))
+- 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

@@ -74,7 +74,6 @@
 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;
@@ -202,11 +201,6 @@ 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);