Shannen Doherty was prepared to die — but that doesn’t mean she was happy about it. The Beverly Hills, 90210, star had things in order ahead of her tragic death on Saturday, July 13, as she unfortunately had years to plan her passing after first being diagnosed with b—– cancer in 2015 that later spread to her brain and bones. “Shannen knew exactly how she wanted to go. She spelled everything out,” a source spilled to a news publication more than one week after Doherty’s devastating death. Doherty had been very open about her health journey with fans, frequently providing updates about her c…