Perhaps the original developer had plans for the future?
There' now real reason to add the fields if they aren't used in a relationship, but check carefully before you delete any fields and make a backup copy first.
You may have multiple table occurrences for the same table here. the _kf fields may be used in a relationship elsewhere than where you first spotted them. One trick to help analyze them is to use the select tables with same source table" option to highlight all occurrences of the same table. (This is an option for the button right next to the zoom percentage box.) You can even use this tool to color code the occurrences so that all with the same source table are the same unique color...