X.Prompt: Remove non-IORef complWin
X.Prompt: Remove non-IORef complWin

While it is true that we need an IORef complWin in case of an exception,
so the window can be destroyed correctly, we do not need its non-IORef
counterpart at all.

When we need to access the complWin it's undoubtably when we want to do
_something_ with regards to window management; these things naturally
live in `XP ()` and so there's not loss of purity with this change.

xmonad/xmonad-contrib,xmonad/xmonad-contrib