Merge core.py with various ...toolbox...py files

In Python, `del` just removes a name from the current namespace. In this case, that namespace is the function `regul_g`, which we are just about to exit anyway, so this is not doing anything.

In general, `del` doesn't directly free memory. It might cause memory to be freed though: If `galaxy_grd` was the only reference to some array, and you did `del galaxy_grd`, then there would be zero references to the array and Python's garbage collector would free the memory the next time it ran.