An old post asked how this type of riser rail could be removed from the wall. The problem being that there are no visible screws or removable end-caps and no parts respond to attempts to unscrew.
I have the same type of riser rail, the same problem (can't see how to remove) and the solution.
After being on the wall for 12 years and subjected to humid conditions parts which should have been removable had become stuck. So I used a small screwdriver and a small toffee-hammer and gently tapped the screwdriver against the junction of the wall and the metal disk in several locations around the perimeter - and found that this disk is a cover which prises off of the mounting plate and exposes the screws holding the rail to the wall - see photos.