Remove Legacy FFI + bindings

[jazzz]

The libchat FFI and nim-bindings are no longer needed after #71 is completed. These enabled the consumption of libchat directly. For the interest of development speed, this is no longer supported and can be removed. Once feature complete appropriate interfaces for the chat core/libchat can be re-added.

• remove FFI at https://github.com/logos-messaging/libchat/blob/main/core/conversations/src/api.rs
• remove nim-bindings.

Notes

• This work cannot be merged until logos-chat-module is updated to use the client interface in this repo.

[jazzz]

Logos-chat is vendored to d006f20 - and is isolated from libchat updates. This work is no longer dependent on logos-chat-module updates, as there ought to be no adverse effects.

[PoulavBhowmick03]

Can I take this up? I have been looking into Logos stack, and have been a part of the office hours, and I came across libchat, would love to get into the codebase by starting with this one!