rm hard-coding of backend Agg

Wrap/Python/ba_plot.py

@@ -14,15 +14,13 @@
 
 import math, os, pathlib, sys
 import bornagain as ba
-try:  # workaround for build servers
+try:
     import numpy as np
     import matplotlib as mpl
-    mpl.use('Agg') # prevent occasional failures, https://stackoverflow.com/a/71511579/1017348
     from matplotlib import rc
     from matplotlib import pyplot as plt
     from matplotlib import gridspec, colors
     from mpl_toolkits.axes_grid1 import make_axes_locatable, axes_size
-
 except Exception as e:
     print(f"Import failure in ba_plot.py: {e}")