[Cashtab] Stop redirecting to /wallet route from cashtab home

Summary:
T3461

The home page isn't really the wallet page. Right now, it shows tx history and balance summary. May change in the future.

Remove hardcoded redirect that always took cashtab.com to /wallet.

Stop using selectedKey var, which is taking location.pathname without the '/'. Instead, use `location.pathname' directly.

Maintain support for cashtab.com/#/wallet in case someone clicks a link there or navigates directly there.

Test Plan:
npm test

npm start, navigate to http://localhost:3000/#/wallet, see normal home page and home icon is eCash blue

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15986