cmd/protoc-gen-go: remove spurious space in "* T"

From:
  func (* T) isT_F() {}

To:
  func (*T) isT_F() {}

Formatting the file removes the space, but the presence or absence of
the space affects the formatter's decision on whether to split the {}
into {\n} or not.

Change-Id: I794c855a3115f9ae1b5f048728d8cad7a5f03e69
Reviewed-on: https://go-review.googlesource.com/c/140637
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -47,7 +47,7 @@ func genOneofTypes(gen *protogen.Plugin, g *protogen.GeneratedFile, f *fileInfo,
 		g.P()
 	}
 	for _, field := range oneof.Fields {
-		g.P("func (* ", fieldOneofType(field), ") ", ifName, "() {}")
+		g.P("func (*", fieldOneofType(field), ") ", ifName, "() {}")
 		g.P()
 	}
 	g.P("func (m *", message.GoIdent.GoName, ") Get", oneof.GoName, "() ", ifName, " {")