If you've already deleted the extensions from /Library/Extensions, open the Terminal app from Launchpad, copy/paste the command below and press Enter to run it:
sudo kextcache -prune-staging
As mentioned in another comment, this will only remove the kernel extensions that are no longer present in their original location, i.e., /Library/Extensions.
The extensions you deleted from /Library/Extensions will then disappear from /Library/StagedExtensions/. It won't affect your other kernel staged extensions.
/Library/StagedExtensions/ is an intermediate area where your extensions live after you start your session (like a cache). The staging area won't be immediately affected if changes are made to /Library/Extensions, which I believe is meant to improve stability and security.
