Stickers, labels and other adhesives can be hard to remove if it's old, has been exposed to high temperatures or is in a humid area. Sticky residue left from bathtub trim fits that description perfectly, but working on small areas at a time with a variety of household products can lead to success in removing the adhesive.
Spray WD-40 on a small area of the sticky residue. Make sure the area is well-ventilated so you don't breathe in the vapours. Let the WD-40 soak in, then use a plastic scraper to remove the residue. Do the same for the next area and continue until the residue is gone. Rinse the WD-40 off with cold water, and clean your bathtub with Soft Scrub to avoid slipping when you get in your tub.
Spread a hand cleaner such as Fast Orange, available in auto stores, on the residue. Carefully scrape the sticky adhesive away with a plastic scraper.
Soak a soft cloth with hot vinegar, and apply it to the adhesive. Let the vinegar soak the sticky residue for 20 minutes, then rub it off.
Mix 1/4 cup of dish soap with 1/2 gallon of warm water. Dip a clean rag in the solution, and rub the sticky area with the rag until the residue is gone.
Open windows and turn on fans. Put on rubber gloves. Dip a rag in lighter fluid, and apply it to the sticky adhesive. Wipe away the residue.
Test all solutions in an inconspicuous area to be sure they don't damage your bathtub.
Read warning labels on all products, and follow the manufacturer's instructions. Use flammable materials in well-ventilated areas.