The rotation code in the draw_arrow function was assuming that the arrow
would be drawn pointing upwards but it was pointing to the right
resulting in the rotated arrows pointing in the wrong direction.

The recent refactoring caused a pi/2 rotation to be lost. Rather than
adding that back somehwere (to lose it again in the future), we just
draw the arrow pointing upwards as it is expected to do with a 0 angle.