make inverse_draw_sample() largely obsolete

nifty4/operators/diagonal_operator.py

nifty4/operators/endomorphic_operator.py

nifty4/operators/inversion_enabler.py

nifty4/operators/operator_adapter.py

nifty4/operators/sandwich_operator.py

nifty4/operators/scaling_operator.py

nifty4/operators/sum_operator.py