A moment of silence, please, for the Organization of African Unity. Born almost 40 years ago in a wave of optimism that Africa could solve its own problems, the OAU never measured up and last week was mercifully killed off by its member states. Its replacement, the African Union, was launched with a whole new set of rules for managing the progress and viability of the continent. While the OAU was formed to fight colonialism, apartheid and foreign interference, the A.U. will concentrate on human rights, democracy, good governance and development.