No. We have suitable bypass conduits in the form of radial arteries (one in each arm) and mammary arteries (one on the left and another on the right) in the chest that can be harvested to do bypass surgery.
Remember, these varicose veins are not healthy and often large (varicose) and not suitable for bypass grafting and likely to clot once they are in place because of the size mismatch and their inflamed (phlebitic) nature.
Finally, chances are in your lifetime that you will get a stent for blockages in your heart rather than bypass surgery.
Those are diseased veins that you would not want your worst enemy to have (or perhaps you would). There is no need to keep this vein, however there is much controversy these days between those that believe treating all the refluxing tributary veins in order to preserve the saphenous veins is the right way to proceed.
Blood will find its own way to your deep venous system without the need for these diseased saphenous veins.
Varicose veins are not suitable for bypass surgery
To use a varicose vein for cardiac bypass surgery would be like putting worn tires that are about to blow onto your car before a cross-country trip. Varicose veins don't have normal strength and they are not used for bypass surgery, so it is safe to get rid of them either through sclerotherapy, endovenous ablation, or surgery (surgery not often necessary these days).