Remove broken caching of area computation results

The problem here is that this code uses the address of the argument as cache key. The argument can however be a temporary, meaning we can get cache key collisions and thus wrong results. This shows in tiles occasionally missing a random subset of polygons, typically in the zoom range 11-15, where we apply area size filters.

The solution is fortunately easy: Remove the caching of the area computation result entirely. We can do this as this neither contributes to the overall cost in a measurable way, nor do we seem to compute the area of the same polygon multiple times anyway.