[GraphBolt] Hacks for old datasets should be cleant up in later version.

## 🔨Work Item

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Project tracker: https://github.com/orgs/dmlc/projects/2

## Description

Old datasets use `seed_nodes` and `node_pairs` in minibatch, while new datasets use `seeds`. DGL will only support `seeds` related operations later, so hacks(#7248) are added for old datasets to confirm that they still can be used in recent versions.

## Depending work items or issues