Import cleanups

nifty4/library/noise_energy.py

@@ -16,7 +16,6 @@
 # NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
 # and financially supported by the Studienstiftung des deutschen Volkes.
 
-from ..field import Field
 from ..sugar import exp
 from ..minimization.energy import Energy
 from ..operators.diagonal_operator import DiagonalOperator