Fix attribute mistake and regenerate code.

csharp/src/Google.Protobuf.Test/TestProtos/UnittestProto3.cs

@@ -786,12 +786,10 @@ namespace Google.Protobuf.TestProtos {
       OneofBytes = 114,
     }
     private OneofFieldOneofCase oneofFieldCase_ = OneofFieldOneofCase.None;
-    [pbr::ProtobufOneof("oneof_field")]
     public OneofFieldOneofCase OneofFieldCase {
       get { return oneofFieldCase_; }
     }
 
-    [pbr::ProtobufOneof("oneof_field")]
     public void ClearOneofField() {
       pb::Freezable.CheckMutable(this);
       oneofFieldCase_ = OneofFieldOneofCase.None;
@@ -4728,12 +4726,10 @@ namespace Google.Protobuf.TestProtos {
       FooMessage = 3,
     }
     private FooOneofCase fooCase_ = FooOneofCase.None;
-    [pbr::ProtobufOneof("foo")]
     public FooOneofCase FooCase {
       get { return fooCase_; }
     }
 
-    [pbr::ProtobufOneof("foo")]
     public void ClearFoo() {
       pb::Freezable.CheckMutable(this);
       fooCase_ = FooOneofCase.None;

csharp/src/Google.Protobuf.Test/TestProtos/UnittestWellKnownTypes.cs

@@ -1592,12 +1592,10 @@ namespace Google.Protobuf.TestProtos {
       BytesField = 18,
     }
     private OneofFieldOneofCase oneofFieldCase_ = OneofFieldOneofCase.None;
-    [pbr::ProtobufOneof("oneof_field")]
     public OneofFieldOneofCase OneofFieldCase {
       get { return oneofFieldCase_; }
     }
 
-    [pbr::ProtobufOneof("oneof_field")]
     public void ClearOneofField() {
       pb::Freezable.CheckMutable(this);
       oneofFieldCase_ = OneofFieldOneofCase.None;

csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs

@@ -295,12 +295,10 @@ namespace Google.Protobuf.WellKnownTypes {
       ListValue = 6,
     }
     private KindOneofCase kindCase_ = KindOneofCase.None;
-    [pbr::ProtobufOneof("kind")]
     public KindOneofCase KindCase {
       get { return kindCase_; }
     }
 
-    [pbr::ProtobufOneof("kind")]
     public void ClearKind() {
       pb::Freezable.CheckMutable(this);
       kindCase_ = KindOneofCase.None;

src/google/protobuf/compiler/csharp/csharp_message.cc

@@ -186,11 +186,9 @@ void MessageGenerator::Generate(io::Printer* printer) {
     printer->Print(
       vars,
       "private $property_name$OneofCase $name$Case_ = $property_name$OneofCase.None;\n"
-      "[pbr::ProtobufOneof(\"$original_name$\")]\n"
       "public $property_name$OneofCase $property_name$Case {\n"
       "  get { return $name$Case_; }\n"
       "}\n\n"
-      "[pbr::ProtobufOneof(\"$original_name$\")]\n"
       "public void Clear$property_name$() {\n"
       "  pb::Freezable.CheckMutable(this);\n"
       "  $name$Case_ = $property_name$OneofCase.None;\n"