chore: remove deprecated billing v2

[zlwaterfield]

Changes

Billing v2 is no longer used. Confirm in request logs for last 30 days. Here is a lighter query for the last 6 hours

This change:

• removes the /billing-v2/ alias url that was left hanging
• updates type names on the client that use BillingV2 preface
• removes some tests
• renames and a few functions

[github-actions[bot]]

Size Change: 0 B

Total Size: 1.06 MB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `frontend/dist/toolbar.js` | 1.06 MB |

_{compressed-size-action}

[posthog-bot]

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[posthog-bot]

📸 UI snapshots have been updated

1 snapshot changes in total. 0 added, 1 modified, 0 deleted:

• chromium: 0 added, 1 modified, 0 deleted (diff for shard 2)
• webkit: 0 added, 0 modified, 0 deleted

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[posthog-bot]

📸 UI snapshots have been updated

1 snapshot changes in total. 0 added, 1 modified, 0 deleted:

• chromium: 0 added, 1 modified, 0 deleted (diff for shard 2)
• webkit: 0 added, 0 modified, 0 deleted

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