Drops the kills that a later write revives: a re-definition cancels a pending named removal of that name,
and any write cancels a wholesale (all/unknown) removal. Used when bubbling kills out of an expression
list so a merging parent only sees the removals still in effect at the list's exit.
Drops the kills that a later write revives: a re-definition cancels a pending
namedremoval of that name, and any write cancels a wholesale (all/unknown) removal. Used when bubbling kills out of an expression list so a merging parent only sees the removals still in effect at the list's exit.