removing unnecessary backend settings

examples/fft/spatial_filter.py

@@ -3,9 +3,6 @@ from __future__ import division
 from __future__ import print_function
 from __future__ import unicode_literals
 
-import matplotlib
-BACKEND = 'Qt4Agg'
-matplotlib.use(BACKEND)
 import pylab as pl
 
 from pykat.optics.gaussian_beams import HG_beam, beam_param