Remove "MQTTv5 only" in documentation comments for MqttClientConnectResult.IsSessionPresent and MqttClientConnectResult.ResultCode (#2166)

* Remove "MQTTv5" from documentation comments for `IsSessionPresent`

 As far as I can tell, this is available for MQTT v3.1.1

References:
* [OASIS Standard](https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718035)
* [MQTTnet source code](https://github.com/dotnet/MQTTnet/blob/93a9d8d1dbe8dde2b7d79a37c873fae13b4f4797/Source/MQTTnet/Connecting/MqttClientConnectResultFactory.cs#L75)

* Remove "MQTTv5 only" for `ResultCode`

Source/MQTTnet/Connecting/MqttClientConnectResult.cs

@@ -30,7 +30,6 @@ public sealed class MqttClientConnectResult
 
     /// <summary>
     ///     Gets a value indicating whether a session was already available or not.
-    ///     MQTTv5 only.
     /// </summary>
     public bool IsSessionPresent { get; internal set; }
 
@@ -58,7 +57,6 @@ public sealed class MqttClientConnectResult
 
     /// <summary>
     ///     Gets the result code.
-    ///     MQTTv5 only.
     /// </summary>
     public MqttClientConnectResultCode ResultCode { get; internal set; }