NEW DELHI — As the rest of India celebrates Hinduism's festival of lights on Tuesday, unscrupulous witch doctors known as “tantriks” will sneak into the country's dark corners to kill some of its rarest and most majestic birds of prey. It's unknown even to most devout Hindus, but the religion's most important holiday, Diwali, marks a supposedly auspicious time for the sacrifices of threatened and even critically endangered owls.