Don't include Haskeline (and others) in the global package DB
GHC installations include
haskeline in their global DB, as well as its dependencies (currently:
terminfo). However, Haskeline isn't a dependency of the
ghc library, so that shouldn't be necessary.
Originally suggested by hvr here, in response to needing to pull
stm into the global DB: https://github.com/judah/haskeline/pull/61\#issuecomment-294878302
This change would let Haskeline add dependencies more easily. See in particular the pending PR to depend on the "exceptions" package: https://github.com/judah/haskeline/pull/97