Revert "[Cashtab] Upgrade react-router-dom to latest version"

Summary:
This reverts commit 7f25a5e77f564e3fad172a11006f3ebc3c5b9142.

prod build is broken from this diff, need to investigate

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15405