Update paho-mqtt to version 2.1.0

[kratz00]

Table of Contents generated with DocToc

• Description
• License Acceptance
• Type of changes
• Checklist

Description

Update to
Small adaptions compared to #203 to get rid of some deprecation warnings.

License Acceptance

• This repository is Apache version 2.0 licensed and by making this PR, I am contributing my changes to the repository under the terms of the Apache 2 license.

Type of changes

• Add/update a helper script
• Add/update link to an external resource like a blog post or video
• Bug fix
• New feature
• Test updates
• Text cleanups/updates

Checklist

• I have read the CONTRIBUTING document.
• All new and existing tests pass.
• Any scripts added use #!/usr/bin/env interpreter instead of potentially platform-specific direct paths (#!/bin/sh is an allowed exception)
• Scripts added/updated in this PR are all marked executable.
• Scripts added/updated in this PR do not have a language file extension unless they are meant to be sourced and not run standalone. No one should have to know if a script was written in bash, python, ruby or whatever. Not including file extensions makes it easier to rewrite the script in another language later without having to change every reference to the previous version.
• I have confirmed that any links added or updated in my PR are valid.