This seemed to be about checking that the user hasn't updated away
when we asked them to resolve merge conflicts. These days we call
cmdutil.checkunfinished() and refuse to update, so the user
shouldn't be able to get into this state.
test-rebase-interruptions.t actually has some tests where it
disables the rebase extension in order to be allowed to do some of
these updates. That still passes, but I wouldn't personally haved
cared if that failed.