By Antony Paone and Richard Lough PARIS (Reuters) -Charles Sobhraj, a convicted killer who police believe killed more than 20 western backpackers on the “hippie trail” through Asia in the 1970s and 1980s, returned to France on Saturday after nearly two decades behind bars in Nepal. Nepal’s Supreme Court ordered the release of Sobhraj, known as the “bikini killer” in Thailand, and ‘The Serpent” for his evasion of police, on Wednesday citing his advanced age and health. A French national who was born to an Indian father and Vietnamese mother, Sobhraj, 78, landed at Paris’ main international airp…