[sv-cc] vpiEndColumn, vpiColumn properties for assertions

I was looking at the assertion diagram and I find these integer properties:
vpiEndColumn, vpiColumn
 
They do not appear in the vpi header file.
Why do we have them? It does not seem necessary and looks like additional 
information which a tool would have to keep.
 
If nobody see a use for them, we should remove them.
 
Francoise
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