Remove unused specialized State instance

core/src/main/scala/cats/state/StateT.scala

@@ -123,7 +123,7 @@ object StateT extends StateTInstances {
     StateT(s => F.pure((s, a)))
 }
 
-private[state] sealed abstract class StateTInstances extends StateTInstances0 {
+private[state] sealed abstract class StateTInstances {
   implicit def stateTMonadState[F[_], S](implicit F: Monad[F]): MonadState[StateT[F, S, ?], S] =
     new MonadState[StateT[F, S, ?], S] {
       def pure[A](a: A): StateT[F, S, A] =
@@ -141,11 +141,6 @@ private[state] sealed abstract class StateTInstances extends StateTInstances0 {
     }
 }
 
-private[state] sealed abstract class StateTInstances0 {
-  implicit def stateMonadState[S]: MonadState[State[S, ?], S] =
-    StateT.stateTMonadState[Eval, S]
-}
-
 // To workaround SI-7139 `object State` needs to be defined inside the package object
 // together with the type alias.
 private[state] abstract class StateFunctions {