[Refactor][Example] Refactor `examples/pytorch/graphsage/advanced`

[yaox12]

🔨Work Item

• [x] Refactor examples/pytorch/graphsage/advanced/train_sampling_unsupervised.py to follow the latest dataloader interface and move it to examples/pytorch/multigpu/multi_gpu_link_prediction.py.
• [x] Remove examples/pytorch/graphsage/advanced/pure_gpu_node_classification.py because it's covered by examples/pytorch/graphsage/node_classification.py.
• [ ] Move examples/pytorch/graphsage/advanced/train_lightning_unsupervised.py to examples/pytorch/graphsage/lightning. Finally remove the examples/pytorch/graphsage/advanced/ directory.

Description

Depending work items or issues

[yaox12]

Reopen this issue because it's partially resolved.

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