List lookup to actual math

"Replaced var/sizes_to_number with weirdass formula that is faster and takes up less space in code than list lookups"

Affected code are all from 5cfa0df3d29a2f631e16e7ee0cc24ab9ca3fe566
**(11-current_size)/2** is being compared to weight *class*. I thought it could mean that weight_class 1 objects are large and heavy, and weight_class 5 objects are the smallest.

Still, after looking through code, it does turn out that weight class directly corresponds with actual size. I'm not exactly sure what to do, this pull request was only meant to be edit in implementation, not functionality/gameplay. I'll remove the comment and let someone else deal with this.