[Cashtab] Bugfix in haveUtxosChanged
[Cashtab] Bugfix in haveUtxosChanged

Summary:
The `haveUtxosChanged` function always returns `true` after it was switched to compare utxo from API against previously saved `wallet.state` utxo set. This means that `hydrateUtxos` is called every 10s, degrading app performance.

This diff returns to the original way of comparing utxo set.

Additionally, the diff simplifies the function by removing redundant and confusing if/else statements.

Test Plan: `npm test`

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9516

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