Remove/Reduce randomness in medical chem healing

[Tarmunora]

codernote: probmult isn't a simple `prob * mult`, the math works out such that if mult is 2, a 10% chance becomes a 19%, but 50% chance becomes only 75%, not 100%, etc etc, which is why where possible we use mult on numbers directly for damage, healing, etc, instead of going through probmult