remove outdated comment

rxd hasn't used scipy in years, so the comment is inaccurate. However, keeping track of contours is not inherently related to rxd, so I'm not sure that there is a better place for this dictionaryt than at the top level.

share/lib/python/neuron/__init__.py

@@ -748,8 +748,6 @@ def _modelview_mechanism_docstrings(dmech, tree):
                 tree.append(line, dmech.location, 0)
 
 
-# TODO: put this someplace else
-#       can't be in rxd because that would break things if no scipy
 _sec_db = {}