### Description
Tracking issue: https://github.com/wormhole-foundation/wormhole-explorer/issues/535.
This pull request fixes an inconsistency between the endpoints `GET /api/v1/x-chain-activity` and `GET /api/v1/top-chain-pairs-by-num-transfers`.
The inconsistency arose because the endpoints computed the data in slightly different ways.
It was resolved by modifying the `GET /api/v1/top-chain-pairs-by-num-transfers` endpoint to use the same data source as `GET /api/v1/x-chain-activity`.
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