Remove location information from Mac Photos seems impossible

There should be a "Remove Location" command in the Image > Location menu, if a photo is selected. It is still there in Photos 4.0:

Add titles, descriptions, and more to photos using Photos on Mac - Apple Support

You can remove a photo’s location information or restore its original location information. 

In the Photos app  on your Mac, select the photos you want to change.

Choose Image > Location, then choose Remove Location or Revert to Original Location.

If you manually assigned location information to a photo that did not have it, Revert to Original Location removes the location information you assigned.

Alternately, you can remove the location information by exporting the image from Photos without the location included. This will wipe the GPS from the exported file and you can reimport it without GPS tags. But I would not throw away the location information for my archived photos. It can be very useful. I remove it only for shared photos.

You can disable the locations for any photos you are sharing from Photos in Photos > Preferences > General.

Probably the user guide needs updating and the command has been renamed to "Hide". I am currently on a Mac with a different system from your system, so I cannot compare this.

Photos never did actually remove the location information, even when the command still used to be called "Remove Location". We could always revert to the original location, even after clicking "Remove location". This just kept Photos from using the location and showing the photos on the map. But photos is always preserving the original image file, exactly as you originally imported it. This lossless workflow is one of the basic design principles of Photos.

If you do not want the GPS information in Photos, even hidden, you have to remove the GPS tags from your photos before you import them to Photos.

You can do this with the Preview.app. Use the "Tools > Show Inspector" menu in Preview. Click the "GPS" tab, then "Remove location".

Or export the photos and import the modified versions.