Remove prompt_conversation and dialogue module

Drop prompt_conversation, collect_text_from_response, Message,
and Dialogue to redesign the conversation feature later.

src/lib.rs

@@ -1,11 +1,9 @@
 mod client;
-mod dialogue;
 pub mod error;
 pub mod network;
 mod types;
 
 pub mod prelude {
     pub use crate::client::*;
-    pub use crate::dialogue::*;
     pub use crate::types::*;
 }