[Cashtab] Remove unused styled import from TokenIcon.js

Summary: Removed unused styled-components import from TokenIcon.js Related to task T2297.

Test Plan: Navigate to /web/cashtab/components/Tokens/TokenIcon.js and ensure styled-components import is removed.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11165