remove scale arg in optimizer

[L1aoXingyu]

• 移除 flow.Optim.xxx Optimizer 里的 scale 参数 定义、文档
• 移除 /test/modules/test_optim_xx 里对 scale 的测试
• 移除 /test/graph/test_graph_optimizer.py 里对 scale 的测试

[github-actions]

CI failed, removing label automerge

[github-actions]

Speed stats:

GPU Name: GeForce GTX 1080 

PyTorch resnet50 time: 137.8ms (= 6888.7ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 125.9ms (= 6297.0ms / 50, input_shape=[16, 3, 224, 224], backward is enabled)
Relative speed: 1.09 (= 137.8ms / 125.9ms)

PyTorch resnet50 time: 82.2ms (= 4107.7ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 72.9ms (= 3645.1ms / 50, input_shape=[8, 3, 224, 224], backward is enabled)
Relative speed: 1.13 (= 82.2ms / 72.9ms)

PyTorch resnet50 time: 56.1ms (= 2802.5ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 47.4ms (= 2369.8ms / 50, input_shape=[4, 3, 224, 224], backward is enabled)
Relative speed: 1.18 (= 56.1ms / 47.4ms)

PyTorch resnet50 time: 48.6ms (= 2428.9ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 49.4ms (= 2472.3ms / 50, input_shape=[2, 3, 224, 224], backward is enabled)
Relative speed: 0.98 (= 48.6ms / 49.4ms)

PyTorch resnet50 time: 40.4ms (= 2017.7ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
OneFlow resnet50 time: 44.8ms (= 2239.0ms / 50, input_shape=[1, 3, 224, 224], backward is enabled)
Relative speed: 0.90 (= 40.4ms / 44.8ms)