missing test_sub_nested_seq_select_layer.protostr

[luotao1]

As rename python/paddle/trainer_config_helpers/tests/configs/{test_seq_select_layers.py => test_sub_nested_seq_select_layer.py} (100%), but test_seq_select_layer.protostr doesn't rename to test_sub_nested_seq_select_layer.protostr, thus, missing protostr for unitest test_sub_nested_seq_select_layer.py.