Silicone sealent is a cross linked polymer and therefore will not dissolve. It may brake down in a strong solution of caustic soda but this is likely to also dammage plastic fittings, grouting and tile finish. I would suggest scrping the surfce of tiles with a sharp razor blade but take car if you try this on a plastic bath. It you try caustic soad TAKE GREAT CARE. This can be extruemly cossosive adn sould never be made up using hot water.
All the best
Hamish
There are chemicals out there specifically designed to remove bathroom sealant - Unibond make one - look in the DIY stores in the same place they sell the sealant - they come in tubes so you will need a sealant gun to apply it