[hotfix] Remove redundant FutureUtils#getFailedFuture

FutureUtils#completedExceptionally does exactly the same.

flink-queryable-state/flink-queryable-state-runtime/src/main/java/org/apache/flink/queryablestate/client/proxy/KvStateClientProxyHandler.java

@@ -169,7 +169,7 @@ public class KvStateClientProxyHandler extends AbstractServerHandler<KvStateRequ
 
 					final InetSocketAddress serverAddress = location.getKvStateServerAddress(keyGroupIndex);
 					if (serverAddress == null) {
-						return FutureUtils.getFailedFuture(new UnknownKvStateKeyGroupLocationException(getServerName()));
+						return FutureUtils.completedExceptionally(new UnknownKvStateKeyGroupLocationException(getServerName()));
 					} else {
 						// Query server
 						final KvStateID kvStateId = location.getKvStateID(keyGroupIndex);

flink-queryable-state/flink-queryable-state-runtime/src/main/java/org/apache/flink/queryablestate/client/proxy/KvStateClientProxyImpl.java

@@ -43,7 +43,7 @@ import java.util.concurrent.CompletableFuture;
 public class KvStateClientProxyImpl extends AbstractServerBase<KvStateRequest, KvStateResponse> implements KvStateClientProxy {
 
 	private static final CompletableFuture<ActorGateway> UNKNOWN_JOB_MANAGER =
-			FutureUtils.getFailedFuture(new UnknownJobManagerException());
+			FutureUtils.completedExceptionally(new UnknownJobManagerException());
 
 	/** Number of threads used to process incoming requests. */
 	private final int queryExecutorThreads;

flink-runtime/src/main/java/org/apache/flink/runtime/concurrent/FutureUtils.java

@@ -445,20 +445,4 @@ public class FutureUtils {
 
 		return result;
 	}
-
-	// ------------------------------------------------------------------------
-	//  Future Completed with an exception.
-	// ------------------------------------------------------------------------
-
-	/**
-	 * Returns a {@link CompletableFuture} that has failed with the exception
-	 * provided as argument.
-	 * @param throwable the exception to fail the future with.
-	 * @return The failed future.
-	 */
-	public static <T> CompletableFuture<T> getFailedFuture(Throwable throwable) {
-		CompletableFuture<T> failedAttempt = new CompletableFuture<>();
-		failedAttempt.completeExceptionally(throwable);
-		return failedAttempt;
-	}
 }