Remove support for string in unmapped_type. (#45675)

This deprecated option was added in 0d8e399 and can now be removed.

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

@@ -770,10 +770,6 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
      * Given a type (eg. long, string, ...), return an anonymous field mapper that can be used for search operations.
      */
     public MappedFieldType unmappedFieldType(String type) {
-        if (type.equals("string")) {
-            deprecationLogger.deprecated("[unmapped_type:string] should be replaced with [unmapped_type:keyword]");
-            type = "keyword";
-        }
         MappedFieldType fieldType = unmappedFieldTypes.get(type);
         if (fieldType == null) {
             final Mapper.TypeParser.ParserContext parserContext = documentMapperParser().parserContext();

server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java

@@ -185,9 +185,6 @@ public class MapperServiceTests extends ESSingleNodeTestCase {
         MapperService mapperService = createIndex("index").mapperService();
         assertThat(mapperService.unmappedFieldType("keyword"), instanceOf(KeywordFieldType.class));
         assertThat(mapperService.unmappedFieldType("long"), instanceOf(NumberFieldType.class));
-        // back compat
-        assertThat(mapperService.unmappedFieldType("string"), instanceOf(KeywordFieldType.class));
-        assertWarnings("[unmapped_type:string] should be replaced with [unmapped_type:keyword]");
     }
 
     public void testPartitionedConstraints() {