Removing a wallet causes the actions to disappear

[j-mueller]

To reproduce

1. load gist accd2826d83e7ce345f8417c06cb7cdd
2. In the "Simulation" tab, remove wallet 3
3. All actions disappear

[krisajenkins]

Whilst this was deliberate....I have been persuaded it's not as great an idea as it seemed at the time. :-D

My thinking was that once you remove a wallet, you can invalidate the simulations, and there's no way in general we can know which actions are now invalid.

However, killing all the simulations is a bit of a, "sledgehammer to crack a walnut," solution, I admit.

I'm going to change this so that the user will have to delete/amend affected actions. They've always been able to submit invalid scenarios, and always been given appropriate feedback when they do.