[Cashtab] Remove api call unit test
[Cashtab] Remove api call unit test

Summary: Unit test was simply checking API response with expected API error msg, no added value

Test Plan: `npm test` passes

Reviewers: #bitcoin_abc, kieran709

Reviewed By: #bitcoin_abc, kieran709

Differential Revision: https://reviews.bitcoinabc.org/D11167

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