Revert "Correct spatialToTrack and getDistances to work in 3D."

This reverts commit 5f15138247b270de7810440d3e3e738bf08dd049.
Correct getDistance and m_line for 3D.

Line joining lower_center to upper_center of quad is now a 3D line.
getDistances is now fixed to return the correct distance of a point from
m_line and with the correct direction.
Change hitLine so that it checks for closeness with a 3D line.
Increase value of m_distance_2 in Item.hpp (needs testing/tweaking)

Increase value of m_distance_2 because distances from a 3D line as
checked in hitLine() can be greater but the kart may still hit the item.
This may need to be tweaked.
Item collection and avoidance now works with 3D tracks!

Also improved AI steering where it would cut corners too aggressively.