Return type: remove one stage of the specialization (#5673)

Author: Tpt

src/impl_/wrap.rs

@@ -21,18 +21,17 @@ impl<T> SomeWrap<T> for Option<T> {
     }
 }
 
-// Hierarchy of conversions used in the `IntoPy` implementation
+// Hierarchy of conversions used in the function return type machinery
 pub struct Converter<T>(EmptyTupleConverter<T>);
 pub struct EmptyTupleConverter<T>(IntoPyObjectConverter<T>);
-pub struct IntoPyObjectConverter<T>(IntoPyConverter<T>);
-pub struct IntoPyConverter<T>(UnknownReturnResultType<T>);
+pub struct IntoPyObjectConverter<T>(UnknownReturnResultType<T>);
 pub struct UnknownReturnResultType<T>(UnknownReturnType<T>);
 pub struct UnknownReturnType<T>(PhantomData<T>);
 
 pub fn converter<T>(_: &T) -> Converter<T> {
-    Converter(EmptyTupleConverter(IntoPyObjectConverter(IntoPyConverter(
+    Converter(EmptyTupleConverter(IntoPyObjectConverter(
         UnknownReturnResultType(UnknownReturnType(PhantomData)),
-    ))))
+    )))
 }
 
 impl<T> Deref for Converter<T> {
@@ -50,13 +49,6 @@ impl<T> Deref for EmptyTupleConverter<T> {
 }
 
 impl<T> Deref for IntoPyObjectConverter<T> {
-    type Target = IntoPyConverter<T>;
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-impl<T> Deref for IntoPyConverter<T> {
     type Target = UnknownReturnResultType<T>;
     fn deref(&self) -> &Self::Target {
         &self.0