remove pad ndim check

[Flowingsun007]

• 修复nn.ZeroPad2d 行为与 pytorch 不一致 vision#234 中遇到的问题

[github-actions]

View latest API docs preview at: https://staging.oneflow.info/docs/Oneflow-Inc/oneflow/pr/8354/

[github-actions]

Speed stats:

GPU Name: NVIDIA GeForce GTX 1080 

❌ OneFlow resnet50 time: 130.3ms (= 13034.1ms / 100, input_shape=[16, 3, 224, 224])
PyTorch resnet50 time: 145.3ms (= 14525.7ms / 100, input_shape=[16, 3, 224, 224])
✔️ Relative speed: 1.11 (= 145.3ms / 130.3ms)

OneFlow resnet50 time: 77.7ms (= 7767.2ms / 100, input_shape=[8, 3, 224, 224])
PyTorch resnet50 time: 90.1ms (= 9014.7ms / 100, input_shape=[8, 3, 224, 224])
✔️ Relative speed: 1.16 (= 90.1ms / 77.7ms)

OneFlow resnet50 time: 55.0ms (= 11005.4ms / 200, input_shape=[4, 3, 224, 224])
PyTorch resnet50 time: 60.5ms (= 12105.1ms / 200, input_shape=[4, 3, 224, 224])
✔️ Relative speed: 1.10 (= 60.5ms / 55.0ms)

OneFlow resnet50 time: 42.9ms (= 8584.4ms / 200, input_shape=[2, 3, 224, 224])
PyTorch resnet50 time: 45.0ms (= 8996.6ms / 200, input_shape=[2, 3, 224, 224])
✔️ Relative speed: 1.05 (= 45.0ms / 42.9ms)

OneFlow resnet50 time: 35.7ms (= 7140.1ms / 200, input_shape=[1, 3, 224, 224])
PyTorch resnet50 time: 37.5ms (= 7496.1ms / 200, input_shape=[1, 3, 224, 224])
✔️ Relative speed: 1.05 (= 37.5ms / 35.7ms)

OneFlow swin dataloader time: 0.242s (= 48.395s / 200, num_workers=1)
PyTorch swin dataloader time: 0.151s (= 30.200s / 200, num_workers=1)
Relative speed: 0.624 (= 0.151s / 0.242s)

OneFlow swin dataloader time: 0.064s (= 12.861s / 200, num_workers=4)
PyTorch swin dataloader time: 0.042s (= 8.409s / 200, num_workers=4)
Relative speed: 0.654 (= 0.042s / 0.064s)

OneFlow swin dataloader time: 0.037s (= 7.476s / 200, num_workers=8)
PyTorch swin dataloader time: 0.023s (= 4.681s / 200, num_workers=8)
Relative speed: 0.626 (= 0.023s / 0.037s)

❌ OneFlow resnet50 time: 146.0ms (= 14599.1ms / 100, input_shape=[16, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 170.2ms (= 17020.9ms / 100, input_shape=[16, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.17 (= 170.2ms / 146.0ms)

OneFlow resnet50 time: 96.9ms (= 9691.2ms / 100, input_shape=[8, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 112.8ms (= 11281.5ms / 100, input_shape=[8, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.16 (= 112.8ms / 96.9ms)

OneFlow resnet50 time: 71.7ms (= 14337.0ms / 200, input_shape=[4, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 87.8ms (= 17561.9ms / 200, input_shape=[4, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.22 (= 87.8ms / 71.7ms)

OneFlow resnet50 time: 60.1ms (= 12018.7ms / 200, input_shape=[2, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 75.0ms (= 14994.7ms / 200, input_shape=[2, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.25 (= 75.0ms / 60.1ms)

OneFlow resnet50 time: 55.3ms (= 11050.3ms / 200, input_shape=[1, 3, 224, 224], ddp, world size=2)
PyTorch resnet50 time: 70.2ms (= 14037.1ms / 200, input_shape=[1, 3, 224, 224], ddp, world size=2)
✔️ Relative speed: 1.27 (= 70.2ms / 55.3ms)