Remove Single-Client API in oneflow default python

[chengtbf]

移除 oneflow 主命名空间 （除去 oneflow.compatible.single_client 之外）内的 Single-Client API。

• refine oneflow.__init__.py
• 移除目录 python/oneflow/advanced/*
• 移除目录 python/oneflow/benchmarks/*
• 移除命名空间 oneflow.checkpoint
• 移除命名空间 oneflow.config 与 目录 python/oneflow/config/*
• 移除目录 python/oneflow/deprecated/*
• 移除命名空间 oneflow.distribute
• 移除命名空间 oneflow.eager （除 oneflow.eager.interpreter_callback 以外的其他内容）
• oneflow.env 只暴露一个 api: all_device_placement
• 移除命名空间 oneflow.experimental （除 oneflow.data.load_mnist）
• 移除 oneflow.framework 下的 blob_trait，checkpoint，compile_context，complier，distribute_context，input_blob_def，interpret_util，local_blob, module，op_util， ops，placement_context，placement_util，pull_util，push_util，remote_blob，scope_symbol，session_util，typing，typing_util，variable_getter_composite，watcher
• 移除命名空间 oneflow.layers
• 移除命名空间 oneflow.math
• 移除目录 python/oneflow/ops/* 中的主要文件（剩余文件后续会迁移到 nn 目录下）
• 移除目录 python/oneflow/optimizer/*
• 移除命名空间 oneflow.random
• 移除命名空间 oneflow.regularizers
• 移除命名空间 oneflow.scope
• 移除命名空间 oneflow.train
• 移除命名空间 oneflow.typing
• 移除命名空间 oneflow.tmp
• 移除命名空间 oneflow.util
• 禁用 oneflow.framework.model
• 禁用 oneflow.saved_model
• 移除 oneflow.framework.check_point_v2 下对 老版本 Eager 的部分
• refine 了 oneflow.framework.unittest，register_class_method_util 的逻辑

[github-actions]

CI failed, removing label automerge

[github-actions]

CI failed, removing label automerge

[github-actions]

Speed stats:

GPU Name: GeForce GTX 1080 

PyTorch resnet50 time: 139.2ms (= 6962.4ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 128.2ms (= 6408.1ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
Relative speed: 1.09 (= 139.2ms / 128.2ms)

PyTorch resnet50 time: 83.8ms (= 4187.9ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 74.6ms (= 3727.6ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
Relative speed: 1.12 (= 83.8ms / 74.6ms)

PyTorch resnet50 time: 61.1ms (= 3057.2ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 47.3ms (= 2366.3ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
Relative speed: 1.29 (= 61.1ms / 47.3ms)

PyTorch resnet50 time: 48.4ms (= 2419.7ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 40.3ms (= 2013.0ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
Relative speed: 1.20 (= 48.4ms / 40.3ms)

PyTorch resnet50 time: 44.2ms (= 2211.6ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 33.6ms (= 1680.9ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
Relative speed: 1.32 (= 44.2ms / 33.6ms)