[Cashtab] Deprecate react-device-detect

Summary: This library was previously used for a legacy QR scanning compatibility issue on iOS devices. This is no longer the case (Apple has opened their API) and the existing width < 769 pixels check is enough to define the platform as mobile, hence deprecating this library.

Test Plan:
grep -r react-device-detect src/ and no outputs
Load react-device-detect.netlify.app on mobile device
Go to send screen and ensure QR code scanner opens camera
Go to send token screen and ensure QR code scanner opens camera
Go to Setting screen and toggle the Auto-Camera open option

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15338