Silence -Wredundant-constraints warnings

In GHC 8.0 -Wall implies -Wredundant-constraints, so we have to
address those warings in one way or another.

cabal-install/Distribution/Client/ComponentDeps.hs

@@ -73,7 +73,7 @@ type ComponentDep a = (Component, a)
 newtype ComponentDeps a = ComponentDeps { unComponentDeps :: Map Component a }
   deriving (Show, Functor, Eq, Ord, Generic)
 
-instance (Semigroup a, Monoid a) => Monoid (ComponentDeps a) where
+instance Semigroup a => Monoid (ComponentDeps a) where
   mempty = ComponentDeps Map.empty
   mappend = (<>)
 

cabal-install/Distribution/Client/FileMonitor.hs

@@ -451,11 +451,13 @@ probeFileSystem root (MonitorStateFileSet singlePaths globPaths) =
       <$> traverseWithKey (probeFileStatus root)     singlePaths
       <*> traverse        (probeGlobStatus root ".") globPaths
 
-traverseWithKey :: (Applicative t, Eq k)
-                => (k -> a -> t b) -> Map k a -> t (Map k b)
 #if MIN_VERSION_containers(0,5,0)
+traverseWithKey :: Applicative t
+                => (k -> a -> t b) -> Map k a -> t (Map k b)
 traverseWithKey = Map.traverseWithKey
 #else
+traverseWithKey :: (Applicative t, Eq k)
+                => (k -> a -> t b) -> Map k a -> t (Map k b)
 traverseWithKey f = fmap Map.fromAscList
                   . traverse (\(k, v) -> (,) k <$> f k v)
                   . Map.toAscList

cabal-install/Distribution/Client/RebuildMonad.hs

@@ -74,7 +74,7 @@ runRebuild (Rebuild action) = evalStateT action []
 --
 -- Do not share 'FileMonitor's between different uses of 'rerunIfChanged'.
 --
-rerunIfChanged :: (Eq a, Binary a, Binary b)
+rerunIfChanged :: (Binary a, Binary b)
                => Verbosity
                -> FilePath
                -> FileMonitor a b