refactor: Expire Time is already set in line 283 (#1996)

Author: MedhaCS1010

google-cloud-spanner/src/test/java/com/google/cloud/spanner/it/slow/ITBackupTest.java

@@ -282,7 +282,6 @@ public void test01_Backups() throws InterruptedException, ExecutionException, Ti
             .setDatabase(database.getId())
             .setExpireTime(expireTime)
             .setVersionTime(versionTime)
-            .setExpireTime(expireTime)
             .setEncryptionConfig(EncryptionConfigs.customerManagedEncryption(keyName))
             .build();
     OperationFuture<Backup, CreateBackupMetadata> operation =