cmd/protoc-gen-go: remove generation of RegisterMessageSetType

PR#741 in the v1 repository deprecated this behavior.

Change-Id: Ife48f1d586f178d875b9b3002a88b3336a2cd3b4
Reviewed-on: https://go-review.googlesource.com/c/151401
Reviewed-by: Damien Neil <dneil@google.com>

cmd/protoc-gen-go/internal_gengo/main.go

@@ -777,13 +777,6 @@ func genInitFunction(gen *protogen.Plugin, g *protogen.GeneratedFile, f *fileInf
 
 func genRegisterExtension(gen *protogen.Plugin, g *protogen.GeneratedFile, f *fileInfo, extension *protogen.Extension) {
 	g.P(protoPackage.Ident("RegisterExtension"), "(", extensionVar(f.File, extension), ")")
-	if name, ok := isExtensionMessageSetElement(extension); ok {
-		goType, pointer := fieldGoType(g, extension)
-		if pointer {
-			goType = "*" + goType
-		}
-		g.P(protoPackage.Ident("RegisterMessageSetType"), "((", goType, ")(nil), ", extension.Desc.Number(), ",", strconv.Quote(string(name)), ")")
-	}
 }
 
 // deprecationComment returns a standard deprecation comment if deprecated is true.

cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go

@@ -755,7 +755,6 @@ func init() {
 	proto.RegisterType((*RepeatedGroup)(nil), "goproto.protoc.extension.ext.RepeatedGroup")
 	proto.RegisterType((*Extendable)(nil), "goproto.protoc.extension.ext.Extendable")
 	proto.RegisterExtension(E_MessageSetWireFormatExtension_MessageSetExtension)
-	proto.RegisterMessageSetType((*MessageSetWireFormatExtension)(nil), 100, "goproto.protoc.extension.ext.MessageSetWireFormatExtension")
 	proto.RegisterType((*MessageSetWireFormatExtension)(nil), "goproto.protoc.extension.ext.MessageSetWireFormatExtension")
 	proto.RegisterExtension(E_ExtensionBool)
 	proto.RegisterExtension(E_ExtensionEnum)
@@ -798,7 +797,6 @@ func init() {
 	proto.RegisterExtension(E_ExtendableField)
 	proto.RegisterExtension(E_ExtendableStringField)
 	proto.RegisterExtension(E_MessageSetExtension)
-	proto.RegisterMessageSetType((*MessageSetWireFormatExtension)(nil), 101, "goproto.protoc.extension.ext.")
 }
 
 func init() { proto.RegisterFile("extensions/ext/ext.proto", fileDescriptor_bf470ef4907b23cb) }