MT#55984 cancel scheduled deletion during offer/answer
Unmark a monologue that has been scheduled for deletion when it's
associated with another one, which happens during offer/answer.
Fixes a regression from 53dbef7e1 which removed this logic from
__monologue_unkernelize with re-adding it elsewhere.
Change-Id: I037162e91fec42631680f7767f58b172fd6e04db