Remove unreachable code in sell()

Remove unreachable code in sell()

sell used to search multiple sectors for sellable commodities, keeping
tally in totalcom.  It failed with message "No eligible" when none
could be found.

sell's second argument got changed to a single sector in Empire 3.  If
the sector can't sell, we return early.  Else, totalcom is positive.
Thus, the "No eligible" code is unreachable.  Remove it.