[P1] util.js: delete dead / test-only exports (Phase 0)

**Parent Epic:** [#44552 — `util.js` decomposition](https://github.com/MetaMask/metamask-extension/issues/44552)
**Source:** `ui/helpers/utils/util.js`
**Size:** S

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## Problem

Ten exports are referenced only in `util.test.js` or nowhere: `formatDateWithSuffix` (+ private `getOrdinalSuffix`), `isDefaultMetaMaskChain`, `addressSummary`, `isOriginContractAddress`, `getRandomFileName`, `checkExistingAllTokens`, `bnLessThan`, `bnGreaterThanEqualTo`, `bnLessThanEqualTo`, `IS_FLASK`. Deleting them shrinks the file with zero import rewrites and de-risks every downstream relocation.

## Solution

Delete the 10 dead/test-only exports, their tests, and any now-unused private helpers. Keep `parseBalance`/`stripOneLayerofNesting`/`stripHttpsScheme` un-exported inside their group's later move.

## Acceptance Criteria

- [ ] 10 exports + dead private helpers removed; `util.test.js` cases for them removed.
- [ ] `yarn lint:tsc` + tests green; zero import-site changes needed.

Start with ui/helpers/utils/util.js and util.test.js. Locate the ten listed exports, their tests, and any now-unused private helpers, then remove those cases without changing import sites. Run yarn lint:tsc and the tests; done means the listed exports and tests are gone and everything remains green.

Written by the indexing model from the issue text.