Avoid NondecreasingIndentation syntax in ghc-pkg

This also makes ghc-pkg.cabal `default-extensions`-free

NB: Printing this commit via `git show --ignore-all-spaces` shows the
    only non-whitespaces changes are in `ghc-pkg.cabal`

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
(cherry picked from commit 913b3146)

Conflicts:
	utils/ghc-pkg/ghc-pkg.cabal