irqtop is a top-like tool for monitoring soft IRQs. It can be quite useful in specific cases but the problem is that it's written in Ruby and we don't have any other Ruby programs in the image. So it adds 30+ megabytes to the image for a rather marginal benefit.

We may replace it with a Python equivalent if there's demand for it, since it's a rather simple frontend for watching files in /proc after all.

There's no operational mode command for it so it can be just removed from the dependencies of vyos-user-utils.