De-allocate memory used by timers on removal

[bjoernQ]

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Submission Checklist 📝

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Pull Request Details 📖

Description

Hopefully fixes #2892

Turned out the memory taken by a timer wasn't de-allocated. (I plan to rewrite timer handling sooner or later, but this should fix it for now)

Testing

Before especially on disconnection / re-connection there was a steady decrease in free memory so you can modify one of the examples accordingly

[bugadani]

Honestly I'm very sad reading code like this, but if it works, it works.

[bjoernQ]

Honestly I'm very sad reading code like this, but if it works, it works.

That whole file makes me sad - I really need to rewrite all of that

[JurajSadel]

Thanks!