Correctly calculate serialized enum style for deserialization

Changes in generated code (see the file attached to PR):
  AdjacentlyTagged, Untagged, Mixed:
    Tuple0: tuple(0) -> unit

    Tuple2as0: tuple(0) -> unit
    Tuple2as1: tuple(1) -> newtype

    Tuple2as0Default: tuple(0) -> unit
    Tuple2as1Default: tuple(1) -> newtype

    Tuple2as0With: tuple(0) -> unit
    Tuple2as1With: tuple(1) -> newtype

serde_derive/src/de.rs

@@ -1910,7 +1910,7 @@ fn deserialize_internally_tagged_variant(
 
     let variant_ident = &variant.ident;
 
-    match effective_style(variant) {
+    match variant.de_style() {
         Style::Unit => {
             let this_value = &params.this_value;
             let type_name = params.type_name();
@@ -1949,7 +1949,7 @@ fn deserialize_untagged_variant(
 
     let variant_ident = &variant.ident;
 
-    match effective_style(variant) {
+    match variant.de_style() {
         Style::Unit => {
             let this_value = &params.this_value;
             let type_name = params.type_name();
@@ -3108,13 +3108,6 @@ fn expr_is_missing(field: &Field, cattrs: &attr::Container) -> Fragment {
     }
 }
 
-fn effective_style(variant: &Variant) -> Style {
-    match variant.style {
-        Style::Newtype if variant.fields[0].attrs.skip_deserializing() => Style::Unit,
-        other => other,
-    }
-}
-
 /// Constructs a tuple variant with default values of all fields
 fn construct_default_tuple(variant: &Variant, cattrs: &attr::Container) -> Option<TokenStream> {
     // Tuple variant with some fields, including newtype variant