Removing stability trigger

Well, this was broken - `add_stability = -1` tried to remove stability from a province, but provinces don't have stability. `owner = { add_stability = -1 }` would be needed to get this effect.

On the other hand, I'd rather just remove it. This event keeps triggering for 50 years with mtth of 16 months. That means any non-Muslim country in the region is going to get (expected) -37.5 stability. Per province. That'd be a ridiculously over the top penalty if it worked, and would basically force them to remain at permanent -3 stability. Increased revolt risk from intolerance + missionary as well as loss of manpower and money are punishment enough.