As feared, the studentd daemon and its mysterious certificate have reappeared, and are now set to remain in Mojave in perpetuity.
If you’ve updated to macOS 10.14.4, you’ve already installed supporting software to use your Mac in a classroom. Was this an error in the update? What does it do?
Have you updated to 10.14.4? Checked your login keychain? You may see a new security certificate there. What’s it for?