add private method _remove_empty_diagonal(), not yet unittested
add private method _remove_empty_diagonal(), not yet unittested

If a diagonal entry is null, and the product is never produced, and the
industry does not produce anything, just completely remove rows and
columns

Could make public if judged useful and unittested

 On branch constructs
 Changes to be committed:
	modified:   pySUT.py

stefanpauliuk/pySUT,NTNU-IndEcol/pySUT,NTNU-IndEcol/pySUT,majeau-bettez/pySUT