Update usage of default value

framework/src/Volo.Abp.EventBus.RabbitMQ/Volo/Abp/EventBus/RabbitMq/AbpRabbitMqEventBusOptions.cs

@@ -14,11 +14,6 @@ public class AbpRabbitMqEventBusOptions
 
     public string ExchangeType { get; set; }
 
-    public AbpRabbitMqEventBusOptions()
-    {
-        ExchangeType = "direct";
-    }
-
     public string GetExchangeTypeOrDefault()
     {
         return string.IsNullOrEmpty(ExchangeType)

framework/src/Volo.Abp.EventBus.RabbitMQ/Volo/Abp/EventBus/RabbitMq/RabbitMqDistributedEventBus.cs

@@ -69,7 +69,7 @@ public class RabbitMqDistributedEventBus : DistributedEventBusBase, ISingletonDe
         Consumer = MessageConsumerFactory.Create(
             new ExchangeDeclareConfiguration(
                 AbpRabbitMqEventBusOptions.ExchangeName,
-                type: AbpRabbitMqEventBusOptions.ExchangeType,
+                type: AbpRabbitMqEventBusOptions.GetExchangeTypeOrDefault(),
                 durable: true
             ),
             new QueueDeclareConfiguration(
@@ -244,7 +244,7 @@ public class RabbitMqDistributedEventBus : DistributedEventBusBase, ISingletonDe
         {
             channel.ExchangeDeclare(
                 AbpRabbitMqEventBusOptions.ExchangeName,
-                AbpRabbitMqEventBusOptions.ExchangeType,
+                AbpRabbitMqEventBusOptions.GetExchangeTypeOrDefault(),
                 durable: true
             );