Remove FeatureFlagSetter.

Replace `FeatureFlagSetter.clear` with `FeatureFlags.TestUtils.reset` in
OpenSearchTestCase tearDown.

Signed-off-by: Finn Carroll <carrofin@amazon.com>

Author: finnegancarroll

test/framework/src/main/java/org/opensearch/test/FeatureFlagSetter.java

@@ -85,6 +85,7 @@
 import org.opensearch.common.time.DateUtils;
 import org.opensearch.common.time.FormatNames;
 import org.opensearch.common.unit.TimeValue;
+import org.opensearch.common.util.FeatureFlags;
 import org.opensearch.common.util.MockBigArrays;
 import org.opensearch.common.util.MockPageCacheRecycler;
 import org.opensearch.common.util.concurrent.ThreadContext;
@@ -242,7 +243,7 @@ public static void resetPortCounter() {
     @Override
     public void tearDown() throws Exception {
         Schedulers.shutdownNow();
-        FeatureFlagSetter.clear();
+        FeatureFlags.TestUtils.reset();
         super.tearDown();
     }