filter out sigs for unused vars
filter out sigs for unused vars

makes verbose output much more readable..

ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ssaavedra/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell,ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell