Remove unnecessary FunctionalDependency

This fixes cobit/bittorrent#7 for GHC 7.8.3: 7.8.3 fixed
FunctionalDependencies so the existing instances are no longer allowed
and in fact FD is not necessary there at all.
Revert "Hide Message, Method, Manager modules", fixes #1

This reverts commit 827a57f66a2ea0087d5eae9de75abae27edbce29.
Merge pull request #2 from Fuuzetsu/fd

Remove unnecessary FunctionalDependency