Ensure destroy callback is set to false.

This builds upon the solution outlined in the previous commit and
the discussion between @zetter, @daniel-rikowski and I[1].

Prior to this commit destroy callbacks would only be run the first time
you attempted to destroy an object, which does not cater for the case
when a call to destroy fails.

This commit addresses this issue, so that destroy callbacks will be
triggered on subsequent calls to `destroy`.

[1] https://github.com/rails/rails/issues/13609