* remove fluid.data

* fix typro

* fix somme unitest error

* fix conflicts

* fix sample code error

* fxi sample coder error

* fxi sample code error

* fxi sample code error

* fix xpu test error

* fix xpu test error

* Delete ps_pb2.py

* fix test error

* fix typro

* fix sample code error

* fix comments

* fix test norm op data

* fix sample code error

* fix conflicts

* support fetch empty tensor on CPUPlace

* fix the shape in unittest of empty output

* remove density_prior_box

* remove anchor_generator

* remove roi_perspective_transform

* remove generate_proposal_labels

* remove generate_mask_labels

* remove generate_proposals

* remove box_clip

* remove retinanet_detection_output

* remove multiclass_nms

* remove locality_aware_nms

* remove matrix_nms

* remove distribute_fpn_proposals

* remove box_decoder_and_assign

* remove collect_fpn_proposals

* remove 2 trt files

* move prior_box to static/nn/common.py

* move multi_box_head to static/nn/common.py

* fix for CI/CE

* remove retinanet_detection_output

* restore compile_vs_runtime_white_list.py

* restore test_retinanet_detection_output to white list

* replace nn.flatten by paddle.flatten, and fix doc for retinanet_target_assign

* add enable_static in demo and fix bug

* remove roi_perspective_transform in test_layers

* remove multi_box_head

* change self.multiclass_nms to _legacy_C_ops.multiclass_nms

* empty commit

* empty commit

* check code style

* fix prior_box

* fix CI

* remove redundant prior_box in detection.py

* fix docs

* remove detection

* fix prior_box en doc

* delete prior_box in common

* remote proir_box from __init__.py

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* phi_matrix_nms

* remove old kernels and add optest check_eager

* reoder args

* reoder args in infermate

* update

* get back legacy dygraph

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* update matrix nms op to api 2.0

* modify code according to review

* Add `matrix_nms_op`

test=develop

* Make ci happy

test=develop

* Exit early when no detection

test=develop

* Fix license year

test=develop

* Output index as well

test=develop

* Match nms2 lod behavior and add `return_index` flag

test=develop

* Make CI happy

test=develop

* Fix wording

test=develop