Can we remove ProtoDataProvider related code?

[luotao1]

Can we remove ProtoDataProvider related codes? Several reasons are as follows:

• ProtoDataProvider has not been used for a long time, and we don't give continuous support and maintenance for it since PaddlePaddle open source.
• In v2 API, we read data using Python API. In v1 API, we read data using PyDataProvider.

@qingqing01 @reyoung @wangkuiyi How do you think about it?

[luotao1]

solved by #5345 and #5775