csrutil disable
Restart computer
In the terminal, type
sudo open /Applications/TextEdit.app /System/Library/LaunchDaemons/com.apple.ManagedClient.enroll.plist
change
<key>com.apple.ManagedClient.enroll</key>
<true/>
to
<key>com.apple.ManagedClient.enroll</key>
<false/>
So that the changes take effect
It looks like 1 of 2 things:
I don't think the enrollment window will reappear because the modifications are on the system files, not a specific user file.
If you already have an admin user, you can choose to modify the script to change the file and have it point towards your admin user (I don't recommend)
Or leave it alone because I don't think having another admin user will affect it.
Disclaimer: I'm just someone reading the script. I have not tested it (planning on it) nor am I the owner or contributor.