SharingService.deletePillarSharee revokes all access to any involved artifacts

SharingService.deletePillarSharee does this:

        # Second delete any access artifact grants.
        ap_grant_flat = getUtility(IAccessPolicyGrantFlatSource)
        to_delete = list(ap_grant_flat.findArtifactsByGrantee(
            sharee, pillar_policies))
        if len(to_delete) > 0:
            accessartifact_grant_source = getUtility(
                IAccessArtifactGrantSource)
            accessartifact_grant_source.revokeByArtifact(to_delete)

So it finds any artifacts that the person has grants on, and then removes every grant to those artifacts -- even grants for other people.