Even if the sound is removed from the QuickTime options, the exported video has sound.
In Toon Boom Studio, in the Timeline view, disable (uncheck) the layer with your sound on it. When you go to make the QuickTime export, you will notice that in the QuickTime options, the Sound option is both unchecked and disabled (greyed out). Your video will now export without sound.
Mac OS X (all)
Toon Boom Studio 5
Toon Boom Studio 6