[dialogs] remove default title

without this removal a user would have to call `SetTitle("")` in order to
erase the default if they desire a title-less dialog.

v3/pkg/application/dialogs.go

@@ -85,7 +85,6 @@ func newMessageDialog(dialogType DialogType) *MessageDialog {
 	return &MessageDialog{
 		MessageDialogOptions: MessageDialogOptions{
 			DialogType: dialogType,
-			Title:      defaultTitles[dialogType],
 		},
 		impl: nil,
 	}