[Remove] Deprecated Synced Flush API (opensearch-project#1761)

Remove the deprecated sync flush API which was replaced by sequence
number and retention lease mechanisms and no longer used in 2.0.0.

Signed-off-by: Nicholas Walter Knize <nknize@apache.org>

client/rest-high-level/src/main/java/org/opensearch/client/IndicesClient.java

@@ -40,7 +40,6 @@
 import org.opensearch.action.admin.indices.delete.DeleteIndexRequest;
 import org.opensearch.action.admin.indices.flush.FlushRequest;
 import org.opensearch.action.admin.indices.flush.FlushResponse;
-import org.opensearch.action.admin.indices.flush.SyncedFlushRequest;
 import org.opensearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.opensearch.action.admin.indices.forcemerge.ForceMergeResponse;
 import org.opensearch.action.admin.indices.open.OpenIndexRequest;
@@ -931,53 +930,6 @@ public Cancellable flushAsync(FlushRequest flushRequest, RequestOptions options,
         );
     }
 
-    /**
-     * Initiate a synced flush manually using the synced flush API.
-     *
-     * @param syncedFlushRequest the request
-     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
-     * @return the response
-     * @throws IOException in case there is a problem sending the request or parsing back the response
-     * @deprecated synced flush is deprecated and will be removed in 8.0.
-     * Use {@link #flush(FlushRequest, RequestOptions)} instead.
-     */
-    @Deprecated
-    public SyncedFlushResponse flushSynced(SyncedFlushRequest syncedFlushRequest, RequestOptions options) throws IOException {
-        return restHighLevelClient.performRequestAndParseEntity(
-            syncedFlushRequest,
-            IndicesRequestConverters::flushSynced,
-            options,
-            SyncedFlushResponse::fromXContent,
-            emptySet()
-        );
-    }
-
-    /**
-     * Asynchronously initiate a synced flush manually using the synced flush API.
-     *
-     * @param syncedFlushRequest the request
-     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
-     * @param listener the listener to be notified upon request completion
-     * @return cancellable that may be used to cancel the request
-     * @deprecated synced flush is deprecated and will be removed in 8.0.
-     * Use {@link #flushAsync(FlushRequest, RequestOptions, ActionListener)} instead.
-     */
-    @Deprecated
-    public Cancellable flushSyncedAsync(
-        SyncedFlushRequest syncedFlushRequest,
-        RequestOptions options,
-        ActionListener<SyncedFlushResponse> listener
-    ) {
-        return restHighLevelClient.performRequestAsyncAndParseEntity(
-            syncedFlushRequest,
-            IndicesRequestConverters::flushSynced,
-            options,
-            SyncedFlushResponse::fromXContent,
-            listener,
-            emptySet()
-        );
-    }
-
     /**
      * Retrieve the settings of one or more indices.
      *

client/rest-high-level/src/main/java/org/opensearch/client/IndicesRequestConverters.java

@@ -42,7 +42,6 @@
 import org.opensearch.action.admin.indices.cache.clear.ClearIndicesCacheRequest;
 import org.opensearch.action.admin.indices.delete.DeleteIndexRequest;
 import org.opensearch.action.admin.indices.flush.FlushRequest;
-import org.opensearch.action.admin.indices.flush.SyncedFlushRequest;
 import org.opensearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.opensearch.action.admin.indices.open.OpenIndexRequest;
 import org.opensearch.action.admin.indices.refresh.RefreshRequest;
@@ -322,15 +321,6 @@ static Request flush(FlushRequest flushRequest) {
         return request;
     }
 
-    static Request flushSynced(SyncedFlushRequest syncedFlushRequest) {
-        String[] indices = syncedFlushRequest.indices() == null ? Strings.EMPTY_ARRAY : syncedFlushRequest.indices();
-        Request request = new Request(HttpPost.METHOD_NAME, RequestConverters.endpoint(indices, "_flush/synced"));
-        RequestConverters.Params parameters = new RequestConverters.Params();
-        parameters.withIndicesOptions(syncedFlushRequest.indicesOptions());
-        request.addParameters(parameters.asMap());
-        return request;
-    }
-
     static Request forceMerge(ForceMergeRequest forceMergeRequest) {
         String[] indices = forceMergeRequest.indices() == null ? Strings.EMPTY_ARRAY : forceMergeRequest.indices();
         Request request = new Request(HttpPost.METHOD_NAME, RequestConverters.endpoint(indices, "_forcemerge"));