4D provides an internal login system based on Users and Groups with Users assigned to Groups and access assigned to the Groups. One of the caveats of creating a Group is that they can not be deleted if not needed anymore.
The best thing to do is to repurpose the group (groups can be renamed) or just ignore them (renaming the group to something later in alphabetical order can help since this will send it to the bottom of the list).
If the group is an Administrator Group Kind there is a way to remove the group, however the Users' passwords may be lost. If a BLOB of Users and Groups or a .4UG file is generated without the undesired Administrator Groups and loaded, the Administrator Groups will be removed. However to generate such data, the BLOB or .4UG must have be created prior to the creation of the Administrator Groups or on a different 4D database meaning the password's assigned to the users may be out of date or that the Users won't even exist and must be recreated without the passwords.