schema cleanup: drop network_total_transactions from checkpoints

[gegaowp]

Description

title, more contexts can be found in https://linear.app/mysten-labs/issue/DP-63/clean-up-network-total-transactions-vs-max-tx-sequence-number-and-min

Test plan

ci to ensure no references to this column any more

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Release notes

Check each box that your changes affect. If none of the boxes relate to your changes, release notes aren't required.

For each box you select, include information after the relevant heading that describes the impact of your changes that a user might notice and any actions they must take to implement updates.

• [ ] Protocol:
• [ ] Nodes (Validators and Full nodes):
• [ ] Indexer:
• [ ] JSON-RPC:
• [ ] GraphQL:
• [ ] CLI:
• [ ] Rust SDK:
• [ ] REST API: