Remove obsolete owner_info API method

[mDuo13]

The owner_info command is an obsolete equivalent to account_objects. (#4404 was the first code change to touch it in ~8 years.) It's undocumented (other than the Public API Methods page saying to not use it).

Unlike account_objects, which supports pagination, ledger selection, filtering, and all types of ledger entries, owner_info only returns lists of Offers and trust lines in the "current" and "accepted" ledgers. (The "accepted" ledger is kind of a legacy equivalent to the "validated" ledger; I'm unclear if there's actually a distinction under the covers.)

I believe you can call this method on p2p nodes from commandline, JSON-RPC, or WebSocket. Clio does not implement this method. I'm unsure about Reporting Mode.

There's no good reason to use owner_info, and I doubt there are any clients actively using it effectively, so we should remove it entirely.

Main source file: https://github.com/XRPLF/rippled/blob/master/src/ripple/rpc/handlers/OwnerInfo.cpp