* cherry & add index_sample op cn doc

* fix index

* update 1.8 apis, test=develop

* udpate contents, test=develop

* add nn.* api

* test=develop

add paddle.complex.tensor.manipulation into gen_doc.sh

* Add Chinese document of API: randn

* add new apis
quote> test=develop

* refine doc
test=develop

* use p
test=develop

* rm no_grad_guard
test=develop

* change fluid site

* change site paddle.*

* add api_cn

* test=develop

* add paddle.tensor

* add

* sync recompute doc btw zh and en, test=document_preview

* test=preview

* change gen_doc

* change gen_doc

* removefill_constant_batch_size_like  gaussian_random_batch_size_like  uniform_random_batch_size_like_cn API doc test=develop

* add disable_dygraph enable_dygraph en cn docs
test=develop

* clean DS_Store
test=develop

* remove FC, test=develop

* delete en_doc for fc, test=develop

* polish code style, test=develop

* change FC to Linear, test=develop

* update index for cn & en doc
* remove duplicated items

add doc for erf into index

add gelu into document index (for both english and chinese doc)

test=develop

* add .rst file of 4 control flow APIs

* add Note in docs of control flow. test=develop

* Add Chinese Doc for cond API

* add Chinese document of control flow API case and switch_case. test=develop

* polish TypeError according to reviews. test=develop

As the title

This reverts commit 6f6cc947.

* add recompute document

* fix-apis-develop

* fix-one-error

fix-contents_cn