[P2] util.js: relocate asset-image helper to asset-utils (dedupe)

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

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## Problem

`getAssetImageURL` (fan-out ~5) is a near-duplicate of `getAssetImageUrl` (lowercase) already in `shared/lib/asset-utils.ts`. This is a dedupe, not just a move — the util.js version has the IPFS try/catch + `logErrorWithMessage` fallback.

## Solution

Reconcile the two into one exported helper in `shared/lib/asset-utils.ts` (preserve the IPFS fallback); rewire the ~5 call sites of the util.js version; delete it.

## Acceptance Criteria

- [ ] Single reconciled helper in `asset-utils.ts`; util.js version deleted; call sites rewired; IPFS-fallback behavior preserved. Tests green.

Start with ui/helpers/utils/util.js and shared/lib/asset-utils.ts, comparing the two asset-image helpers and tracing the roughly five call sites of the util.js version. Reconcile them in asset-utils.ts while preserving the IPFS fallback, remove the old helper, and run the relevant tests to confirm all tests are green.

Written by the indexing model from the issue text.