fix(pynml): remove new imported sub-module

`nsgr` should not be imported into pynml.

Author: sanjayankur31

pyneuroml/pynml.py

@@ -32,7 +32,6 @@
 from pyneuroml.runners import *
 from pyneuroml.validators import *
 from pyneuroml.annotations import *
-from pyneuroml.nsgr import *
 from pyneuroml.io import *
 from pyneuroml.utils.info import *