Remove --c-files from extraOptions
Remove --c-files from extraOptions

Fixes #1586.

This commit removes the --c-files options from extraOptions, as this was
causing symbols to be loaded twice by the linker when running the tests
via Cabal.

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