I wouldn't worry at all. Wd40 will evaporate alsomost entirely leaving a light residue of paraffin wax. The problem is it is not a lubricant it is a cleaner and it has removed all the old oils and grease leaving what ever steel/chrome it touched vulnerable to corrosion. If you do nothing, the residue will wear off after a few hard brakings. If you must, a little mineral spirits will remove the wax residue (brake pads and the brake surface on the rim). You may want to spray any exposed steel or chrome surfaces with Pledge polish, which a silicone product and it also makes frame paint really shine! Good Luck.