[Cashtab] Remove faulty unit tests

Summary:
While it would be nice to have automated integration tests like these -- these tests are not actually doing what they say they are doing. That they pass is misleading.

To properly automate integration tests in hooks, we need

• localforage mock
• different libraries with access to full component state

Remaining unit tests in useWallet.js are testing functions from the hook.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15104