Prunella Scales, the British actress best known for her role as Sybil Fawlty in the BBC sitcom “Fawlty Towers,” has died. She was 93. Her sons, Samuel and Joseph West, confirmed to The Post she died “peacefully at home in London” on Monday. She was diagnosed with vascular dementia in 2013. The boys also revealed that Scales was watching “Fawlty Towers” the day before she died. “Although dementia forced her retirement from a remarkable acting career of nearly 70 years, she continued to live at