JOHANNESBURG — Blackened by soot, the gutted and derelict remains of South Africa’s infamous Usindiso building in central Johannesburg are an unintentional memorial to the 76 people who died hereJOHANNESBURG — Blackened by soot, the gutted and derelict remains of South Africa’s infamous Usindiso building in central Johannesburg are an unintentional memorial to the 76 people who died here