Slxu kill cleanup

Clean up system resources, especially network resources when a query is killed.
The name of this function is a bit misleading. It looks like it's being used as `getOrAllocateInbutBuffer`... but actually, when I look at how it's used, it looks more like you always expect to allocate in `LocalFragmentResourceManager` and you always expect to get in `Consumer`.

Maybe we should refactor it into a get and an allocate function, and verify the implicit assumptions that way? This would let us be sure that our mental model of what's happening is correct.