Ceiling joists job in a cinder block house
Ceiling joists don't necessarily hold up the walls. What they do is prevent the outward force of the roof pushing the walls out. The joists 'pull' the outward forces together canceling them out so that the only force on the walls is then downwards. 

Whether your walls are stick frames or masonry, they're strength is in compression from downward forces rather than deflection from outward forces. 

If you're planning on removing the ceiling joists, you will need to replace them with something. Beams could work as could steel cables. 

Alternatively, you could install a ridge joist. A ridge joist is supports by columns down to the foundation and will carry the weight of the roof.