The question at hand is:
How to completely remove (purge) unused (removed via GUI) kernel packages in Linux Mint 18.x after man removes these kernels via Mint Update Manager -> Linux Kernels window?
As you can see below, there is only one kernel installed, I have removed all others:
Since they were removed, I presumed they were purged completely, but I was wrong. Once I did:
dpkg --list | grep "linux-image"
There was more like 30 packages with rc prefix.