remove unamed

When you select the textfield "Unnamed", are you seeing a circle with an "x" on the periphery? If yes, click the "x" to remove the circle. In the earlier versions of Photos you could remove automatically detected faces this way. But this changed somewhere around the macOS Sierra 10.12.6 release. It may already be too late for you. In the current versions of Photos is no way to remove unwanted, automatically detected faces. We can only disable the display of the detected faces completely as shown by Mark.

You can turn off all people name overlays (including "Unnamed") by choosing View > Hide Face Names.

If you wanted to suppress only the "Unnamed" names, I don't know of a way to do that.