There are a couple of reports of the same thing, and I'm seeing it myself on one machine.
Skype is now installed as standard with Windows, and so as Nergal say it is more or less built-in to Windows now.
For whatever reason the CCleaner Software Updater is now still seeing some remnant of Skype after it has been uninstalled, and so thinks that you still have it installed.
I’m not sure if that’s started happening because a change that Windows has made, or a change to the CCleaner Software Updater?
Not that it really matters here, whatever has changed it’s happening.
I'd suggest that you just reinstall Skype and then ignore it.
That’s what I’m going to do on that machine where I’m seeing this.
Let's face it Windows puts a lot of 'standard' apps on our machines that most of us will never use, 3D Builder, Game Bar, Mixed Reality Portal, etc, etc. not forgetting the whole 'Windows Accessories' section.
Skype is just another one of those ‘standard’ apps now, so even if you never use it I’d just leave it there and ignore it.