[Docathon][Update Doc No.21-34] remove all the related files

[Abosite]

remove the following files:
docs/api_guides/low_level/layers/activations_en.rst
docs/api_guides/low_level/layers/activations.rst
docs/api_guides/low_level/layers/control_flow_en.rst
docs/api_guides/low_level/layers/control_flow.rst
docs/api_guides/low_level/layers/conv_en.rst
docs/api_guides/low_level/layers/conv.rst
docs/api_guides/low_level/layers/data_feeder_en.rst
docs/api_guides/low_level/layers/data_feeder.rst
docs/api_guides/low_level/layers/data_in_out_en.rst
docs/api_guides/low_level/layers/data_in_out.rst
docs/api_guides/low_level/layers/detection_en.rst
docs/api_guides/low_level/layers/detection.rst
docs/api_guides/low_level/layers/index_en.rst
docs/api_guides/low_level/layers/index.rst
docs/api_guides/low_level/layers/learning_rate_scheduler_en.rst
docs/api_guides/low_level/layers/learning_rate_scheduler.rst
docs/api_guides/low_level/layers/loss_function_en.rst
docs/api_guides/low_level/layers/loss_function.rst
docs/api_guides/low_level/layers/math_en.rst
docs/api_guides/low_level/layers/math.rst
docs/api_guides/low_level/layers/pooling_en.rst
docs/api_guides/low_level/layers/pooling.rst
docs/api_guides/low_level/layers/sequence_en.rst
docs/api_guides/low_level/layers/sequence.rst
docs/api_guides/low_level/layers/sparse_update_en.rst
docs/api_guides/low_level/layers/sparse_update.rst
docs/api_guides/low_level/layers/tensor_en.rst
docs/api_guides/low_level/layers/tensor.rst

• Paddle主框架文档修复任务，速来！ Paddle#71203

@DrRyanHuang 和 @sunzhongkai588

[paddle-bot]

感谢你贡献飞桨文档，文档预览构建中，Docs-New 跑完后即可预览，预览链接：http://preview-pr-7080.paddle-docs-preview.paddlepaddle.org.cn/documentation/docs/zh/api/index_cn.html
预览工具的更多说明，请参考：飞桨文档预览工具

[DrRyanHuang]

请依次查找，以下文件是否被其他文件所引用，如果有，则删除对应文档的引用后，再删除该文件

[DrRyanHuang]

@Abosite 感谢同学认领了这么多题目🥳，除了删除源文件，也要删除对应的引用

同学可以先删除这些引用比较少的文档

docs/api_guides/low_level/layers/control_flow.rst
docs/api_guides/low_level/layers/data_feeder.rst
docs/api_guides/low_level/layers/data_in_out.rst
docs/api_guides/low_level/layers/detection.rst
docs/api_guides/low_level/layers/math.rst
docs/api_guides/low_level/layers/sequence.rst
docs/api_guides/low_level/layers/sparse_update.rst
docs/api_guides/low_level/layers/tensor.rst

以下这部分文档不能直接删除，要先看有哪些文档引用，以及是否适合删除，将过时不必要的内容删除

docs/api_guides/low_level/layers/activations.rst
docs/api_guides/low_level/layers/conv.rst
docs/api_guides/low_level/layers/index.rst
docs/api_guides/low_level/layers/learning_rate_scheduler.rst
docs/api_guides/low_level/layers/loss_function.rst
docs/api_guides/low_level/layers/pooling.rst

[Abosite]

@Abosite 感谢同学认领了这么多题目🥳，除了删除源文件，也要删除对应的引用

同学可以先删除这些引用比较少的文档

docs/api_guides/low_level/layers/control_flow.rst
docs/api_guides/low_level/layers/data_feeder.rst
docs/api_guides/low_level/layers/data_in_out.rst
docs/api_guides/low_level/layers/detection.rst
docs/api_guides/low_level/layers/math.rst
docs/api_guides/low_level/layers/sequence.rst
docs/api_guides/low_level/layers/sparse_update.rst
docs/api_guides/low_level/layers/tensor.rst

以下这部分文档不能直接删除，要先看有哪些文档引用，以及是否适合删除，将过时不必要的内容删除

docs/api_guides/low_level/layers/activations.rst
docs/api_guides/low_level/layers/conv.rst
docs/api_guides/low_level/layers/index.rst
docs/api_guides/low_level/layers/learning_rate_scheduler.rst
docs/api_guides/low_level/layers/loss_function.rst
docs/api_guides/low_level/layers/pooling.rst

感谢您的回复！我将依次进行检查。

[DrRyanHuang]

PS: 如果一个PR对应的改动文件太多，会导致Github页面很卡顿，之后可以分开提PR

[Abosite]

PS: 如果一个PR对应的改动文件太多，会导致Github页面很卡顿，之后可以分开提PR

好的，我将关闭这个PR并依次提交。