remove old tutorial script machinery

doc/source/code/README

doc/source/code/figure/_defs.py

doc/source/code/figure/ab_ring.py.diff

doc/source/code/figure/ab_ring_sketch.svg

doc/source/code/figure/ab_ring_sketch2.svg

doc/source/code/figure/band_structure.py.diff

doc/source/code/figure/closed_system.py.diff

doc/source/code/figure/discretize.py.diff

doc/source/code/figure/faq.py.diff

doc/source/code/figure/graphene.py.diff

doc/source/code/figure/kernel_polynomial_method.py.diff

doc/source/code/figure/magnetic_texture.py.diff

doc/source/code/figure/plot_graphene.py.diff

doc/source/code/figure/plot_qahe.py.diff

doc/source/code/figure/plot_zincblende.py.diff

doc/source/code/figure/quantum_well.py.diff

doc/source/code/figure/quantum_wire.py.diff

doc/source/code/figure/spin_orbit.py.diff

doc/source/code/figure/superconductor.py.diff

doc/source/code/figure/superconductor_transport_sketch.svg