4-Aza-3-oxo-5.alpha.-androst-1-ene-17.beta.-N-arylcarboxamides as Dual Inhibitors of Human Type 1 and Type 2 Steroid 5.alpha.-Reductases. Dramatic Effect of N-Aryl Substituents on Type 1 and Type 2 5.alpha.-Reductase Inhibitory Potency