[Cashtab] Remove support for sending to BCH or SLP addresses

Summary:
T1735

Remove support for sending to addresses with bitcoincash: or simpleledger: prefixes, even if they are valid cashaddr.

This diff also modifies validation so that xec must be sent to an ecash: prefixed address and eTokens must be sent to an etoken: prefixed address.

Test Plan: npm start, try to send XEC to a bitcoincash: prefixed address and an etoken: prefixed address and note validation, try to send eToken to simpleledger: prefixed address and ecash: prefixed address and note validation

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9883