remove center_last functionality
remove center_last functionality

We decided there is no real use for this as a user setting.
The center walls are currently always printed after their enclosing walls.
Printing all center walls after all normal walls means that all the centers and normal walls aren't interspersed.
This was hypothesized to lead to less flow changes during printing of the walls.
However, we didn't want to test this and we didn't want to confuse the user with more settings.

Ultimaker/CuraEngine,Ultimaker/CuraEngine