remove shotrad4 case in shotrad because it doesn't exist

gwinc/noise/quantum.py

@@ -63,11 +63,7 @@ def shotrad(f, ifo, mirror_mass, power):
 
     # deal with non-standard number of fields
     if Nfield != 2:
-        if Nfield == 4:
-            n = shotrad4(f, ifo, coeff, Mifo, Msig, Mn)
-            return n
-        else:
-            raise Exception("shotrad doesn't know what to do with %d fields" % Nfield)
+        raise Exception("shotrad doesn't know what to do with %d fields" % Nfield)
 
     #####################################################
     # Input Squeezing