The .view (and possibly .prev_view) would be kept attached to the
removed zone until the zone is fully removed from the memory in
zone_free(). If this process is delayed because server is busy
something else like doing constant `rndc reconfig`, it could take
seconds to detach the view, possibly keeping multiple dead views in the
memory. This could quickly lead to a massive memory bloat.
Release the views early in the zone_shutdown() call, and don't wait
until the zone is freed.
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