Avoid duplicated warnings
Avoid duplicated warnings

This commit suppresses all warnings in `GhcMonadLike.typecheckModule`,
avoiding that any GHC warning issued as the result of typechecking a
particular module would be printed twice, once by GHC itself and once by
the plugin.

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