panel item remove confirmation

[Jannis Pohlmann]

> I see Jannis mentioned a "Don't ask me again"-type dialog, which I like,
> but it breaks the usual behavior a bit.  Usually they imply "... and do
> what I did this time from now on".  But of course, checking it and then
> clicking "cancel" is absurd: then you can never remove panel items.

Oops, haha. Indeed, I must have forgotten about that ...

- Jannis