[Cashtab] Replace SLP with eToken in token tx notification

Summary:
T1761

Remove hardcoded 'SLP' and replace with 'eToken' as variable from Ticker.js

Test Plan: npm start, receive a tx, notification says 'eToken' instead of 'SLP'

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9909