[Cashtab] Change default setting for camera auto-open

Summary:
In practice I don't think this is a popular feature. More likely to confuse user than streamline sendign to QR codes.

But, for users who do want to streamline sending to QR codes, they can enable it.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D17593