remove superfluous import

nifty/operators/diagonal_operator/diagonal_operator.py

@@ -21,7 +21,6 @@ import numpy as np
 from d2o import distributed_data_object,\
                 STRATEGIES as DISTRIBUTION_STRATEGIES
 
-from nifty.basic_arithmetics import log as nifty_log
 from nifty.config import nifty_configuration as gc
 from nifty.field import Field
 from nifty.operators.endomorphic_operator import EndomorphicOperator