[Cashtab] Patch header links to token page in extension

Summary: Noticed these links are busted in the prod extension. Remove the '/', and they work in webapp and extension.

Test Plan: npm start, header links to token pages work, npm run extension, load unpacked, they work in extension too

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17786