Remove dead window if its activity record is cleared from history

We keep the dead window if its activity record is kept. However, if
the activity doesn't have any saved state, the record will be removed
too, in that case we have to remove that window.

And add a "apps" option in window dump to retrieve all app windows
regardless of the visible states. We need this to get the windows
that's waiting for replacements.

bug: 26324082

Change-Id: I7179354fe85553a5436b26371d3ad7295a452ce3