fix: remove unused and buggy instances of semigroup for dependency

src/Stack/Types/Dependency.hs

@@ -10,7 +10,6 @@ module Stack.Types.Dependency
 import qualified Distribution.PackageDescription as Cabal
 import           Distribution.Types.VersionRange ( VersionRange )
 import           Stack.Prelude
-import           Stack.Types.Version ( intersectVersionRanges )
 
 -- | The value for a map from dependency name. This contains both the version
 -- range and the type of dependency, and provides a semigroup instance.
@@ -20,9 +19,6 @@ data DepValue = DepValue
   }
   deriving (Show, Typeable)
 
-instance Semigroup DepValue where
-  DepValue a x <> DepValue b y = DepValue (intersectVersionRanges a b) (x <> y)
-
 -- | Is this package being used as a library, or just as a build tool? If the
 -- former, we need to ensure that a library actually exists. See
 -- <https://github.com/commercialhaskell/stack/issues/2195>
@@ -31,10 +27,6 @@ data DepType
   | AsBuildTool
   deriving (Eq, Show)
 
-instance Semigroup DepType where
-  AsLibrary <> _ = AsLibrary
-  AsBuildTool <> x = x
-
 cabalToStackDep :: Cabal.Dependency -> DepValue
 cabalToStackDep (Cabal.Dependency _ verRange _libNameSet) =
   DepValue{dvVersionRange = verRange, dvType = AsLibrary}