Remove MetaSwap Liveliness Polling

Per: https://www.notion.so/airswap/Reduce-featureFlag-load-0fd49db2f87641cda7600c33b3eae9af

The `/featureFlag` endpoint of MetaSwap is bogging down MetaSwap's logging due the 10 minute polling done here:

https://github.com/MetaMask/metamask-extension/blob/develop/app/scripts/controllers/swaps.js#L635-L723

The MetaSwap team has asked us to remove this polling. Since we check the feature flag via `fetchSwapsFeatureLiveness()` at the time we request a quote, this polling appears to be unnecessary. This code does give us online/offline event support, so maybe we can more efficiently get liveliness data.

Start by reading app/scripts/controllers/swaps.js around lines 635-723 and trace the existing 10-minute polling alongside fetchSwapsFeatureLiveness(). Confirm how quote requests check the feature flag and how online/offline events are used; done means removing the unnecessary polling while preserving the required liveness behavior.

Written by the indexing model from the issue text.