Simplify logic for showing per-channel results

As Jonas pointed out, the code used to contain a check for non-nan
values, effectively skipping channels where the Raman gain was not
explicitly computed.

Now that we do not introduce NaNs into some channels anymore, this
shortcut no longer works. We could either add explicit filtering for
only showing those channels which are covered by the Raman engine, but
then the result would be rather confusing in the non-Raman case. One
could also add another column with the simulated vs. approximated NLI,
but when I tried this, the output looked a bit cluttered.

I think that the best course of action for now is to just show info
about all channels (if asked by the user). So this is just a cleanup for
a condition which is now always on.

examples/transmission_main_example.py

@@ -18,7 +18,7 @@ from pathlib import Path
 from json import loads
 from collections import Counter
 from logging import getLogger, basicConfig, INFO, ERROR, DEBUG
-from numpy import linspace, mean, log10, isnan
+from numpy import linspace, mean, log10
 from matplotlib.pyplot import show, axis, figure, title, text
 from networkx import (draw_networkx_nodes, draw_networkx_edges,
                       draw_networkx_labels, dijkstra_path)
@@ -299,9 +299,8 @@ if __name__ == '__main__':
             ch_power = 10 * log10(final_carrier.power.signal)
             ch_snr_nl =  ch_power - 10 * log10(final_carrier.power.nli)
             ch_snr = ch_power - 10 * log10(final_carrier.power.nli + final_carrier.power.ase)
-            if not isnan(ch_snr):
-                print(f'{final_carrier.channel_number} \t\t {round(ch_freq, 2):.2f} \t\t\t {round(ch_snr_nl, 2):.2f} '
-                      f'\t\t\t\t {round(ch_snr, 2):.2f}')
+            print(f'{final_carrier.channel_number} \t\t {round(ch_freq, 2):.2f} \t\t\t {round(ch_snr_nl, 2):.2f} '
+                  f'\t\t\t\t {round(ch_snr, 2):.2f}')
 
     if not args.source:
         print(f'\n(No source node specified: picked {source.uid})')