how to remove a legacy system extension

You should always wait a few iterations of a new OS to get the bugs worked out, that's likely a year from now!

No need to worry, but to see them, just don't upgrade to 10.16 if the developers don't have updates...

About this Mac>System Report>Software>Extensions, click on Obtained from Header, all that aren't Apple are Legacy.

You don't need to do anything right now. It's just a warning that such extensions will not work if you install the upcoming macOS upgrade, Big Sur. Logitech will have to release new software that works with the new OS.

If you don't upgrade to Big Sur, you won't have to do anything. Other than dismiss the warning message once a month.

Do you need to remove it, or are you responding to a message that it will be unsupported in the next OS?

Remove a legacy system extension