fix tests; remove old code

Author: markjhoy

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapper.java

@@ -455,6 +455,10 @@ private void validateIndexOptions(SemanticTextIndexOptions indexOptions, String
                 return;
             }
 
+            if (indexOptions.type() == SemanticTextIndexOptions.SupportedIndexOptions.SPARSE_VECTOR && modelSettings == null) {
+                return;
+            }
+
             if (modelSettings == null) {
                 throw new IllegalArgumentException(
                     "Model settings must be set to validate index options for inference ID [" + inferenceId + "]"

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapperTests.java

@@ -198,19 +198,6 @@ private static void validateIndexVersion(IndexVersion indexVersion, boolean useL
         }
     }
 
-    /*
-    private MapperService createMapperService(String mappings, boolean useLegacyFormat) throws IOException {
-        var settings = Settings.builder()
-            .put(
-                IndexMetadata.SETTING_INDEX_VERSION_CREATED.getKey(),
-                SemanticInferenceMetadataFieldsMapperTests.getRandomCompatibleIndexVersion(useLegacyFormat)
-            )
-            .put(InferenceMetadataFieldsMapper.USE_LEGACY_SEMANTIC_TEXT_FORMAT.getKey(), useLegacyFormat)
-            .build();
-        return createMapperService(settings, mappings);
-    }
-     */
-
     @Override
     protected Settings getIndexSettings() {
         return Settings.builder()