Drop MQTT will related settings parameters

[ckrey]

Instead as in the Android app:

• always use will
• willTopic is the same as pubTopicBase after User/Device replacements
• willQos is the same as pubQos
• willRetain is always false

[ckrey]

otherwise, we will have to add to the docs:

[jpmens]

I'm for standardizing on these four settings and removing their 'configurability' from the app.

[ckrey]

Included in 17.2.5