Remove MaximumQoS property from CONNECT packet #161

[tomatod]

Do not create a Pull Request without creating an issue first
#161 was created related to this request.

The design of your solution to the problem should be discussed and agreed in an issue before submitting the PR
According to MQTTv5 spec, Maximum QoS property should not be included in CONNECT packet. Actually, when I tried to send CONNECT packet included that property to Mosquitto MQTT server, the connection was refused by Mosquitto. So, I think we should remove Maximum QoS property from CONNECT packet in this library.

note: This request is same with #240, but I remaked the request after some confirmations, because there was a problem with test on my envrionment (#242). As a result, the problem wasn't probably related to this change.

ECA - Eclipse Contributer Agreement
had already done

Testing

• make test was passed. I sometimes catched an issue with An autopaho test TestQueuedMessage may be not passed. #242, but tests were passed temporarily with making the timeout of autopaho's cm longer.
• I confirmed almost all parts related to this change with grep ''QOS" or "QoS" (including "MaximumQoS" and "MaximumQOS") just in case.

Closing issues
closes #161

[MattBrittan]

Thanks very much for submitting this.