Los Angeles (AFP) – Singer Olivia Newton-John, who gained worldwide fame as high school sweetheart Sandy in the hit musical movie “Grease,” died on Monday after a 30-year battle with cancer. She was 73. Newton-John “passed away peacefully at her ranch in Southern California this morning, surrounded by family and friends,” said a statement from her husband John Easterling posted on her official social media accounts. The multiple Grammy-winning entertainer, whose career spanned more than five decades, including chart-topping songs such as “Physical,” devoted much of her time in later years to c…