remove unused local variables

Author: rxng8

ngclearn/utils/model_utils.py

@@ -91,7 +91,6 @@ def create_function(fun_name, args=None):
     elif fun_name == "sine":
         fx = sine
         dfx = d_sine
-        omega_0 = args
     elif fun_name == "sigmoid":
         fx = sigmoid
         dfx = d_sigmoid