How to remove spurious entries for Silverlight in Registry

Ignore them.

There is absolutely no need to "clean" the Windows Registry, and if you are not completely familiar with the inner workings of the registry (and few, other than some Microsoft engineers are), the likelihood of doing significant, perhaps irreversible, damage to your system is high.

Frankly, I'm really surprised that you received even an optional update for Silverlight.

Silverlight was Microsoft's attempt to compete with Adobe Flash (which itself is now no longer supported), but was never particularly successful.  I believe that Microsoft "deprecated" (essentially abandoned) Silverlight as long ago as 2015.  The only web browser that still uses Silverlight (until October 21 of this year) is Internet Explorer 11 -- and Microsoft has been urging people to drop IE 11 for years (IE 11 end of life is this August).

As ElderN suggests, it seems that you had already installed an old version of Silverlight (4.x), so you probably were being offered an update to the current version, Silverlight 5.  Did you take a look for Silverlight in "Programs and Features" (click Start, type appwiz.cpl in the Search box, and press Enter)?

And if other companies' software didn't also clutter up the Windows Registry, there wouldn't be so many registry cleaners and optimizers for ElderN to have tried.

If you decided not to install Silverlight and then see/saw entries for it in the registry how do you know the entries were not there before if Silverlight was not installed?

I have used just about every remotely popular registry cleaner/optimizer from the Internet and have never had a problem...

But I always make a manual restore point and backup the registry before starting so if something goes haywire I know I can undo things.  If my system won't boot or malfunctions afterwards I don't care because I know I can fix it.

I have also done many timing test of before/after boot times, etc. and I might have save some milliseconds which isn't much and may not be "worth it" if you are a worry wart and don't know how to plan for problems.

But I don't like the clutter either and MS is certainly notorious for leaving a registry mess behind when some of their stuff installs - which was the reason I have tested so many cleaner/optimizers.

I can't stand that mess on some of their uninstalls.

Curious  - this issue of Microsoft install/uninstall leaving lots of files & registery entries cluttering up the system has been reported often - especially re Silverlight and language files!
Thankfully not the case with other companies software.

In future I shall think thrice before installing Microsoft updates - especially as I now see Silverlight support is soon to be ended! So why did MS update offer Silverlight as an update to Windows 7 when support of Win 7 ended a year ago?

Yet another attempt to force me to change to Windows 10?? NB. had to crash my PC to stop that so-called "optional" update.

PS. Anyone have a solution to my question?

Lem has advised you well.  I second the statement.