[Cashtab] Remove unimplemented agora methods

Summary:
These methods were necessary to implement NFT trading using LOKAD ID to get all information about active offers. Recent upgrades to ecash-agora have made this method obsolete.

See D16328. Cashtab is now able to get these methods without specialized agora parsing.

Remove it.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16738