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

[yxy235]

🔨Work Item

IMPORTANT:

• This template is only for dev team to track project progress. For feature request or bug report, please use the corresponding issue templates.
• DO NOT create a new work item if the purpose is to fix an existing issue or feature request. We will directly use the issue in the project tracker.

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