api!: Remove unused info_only option when loading a chatlist (#8171)

Remove unused info_only option from `get_chat_msgs_ex()`.

This option was meant to show an "audit log" of a group, i.e. only the
info messages. This feature was removed again from Desktop, but the
option still lingered around in Core.

This also adds a doc comment to the JsonRPC functions, because I
wanted to note somewhere that the parameter is deprecated, and I needed
some place to put this note.

deltachat-repl/src/cmdline.rs

@@ -622,7 +622,6 @@ pub async fn cmdline(context: Context, line: &str, chat_id: &mut ChatId) -> Resu
                 &context,
                 sel_chat.get_id(),
                 chat::MessageListOptions {
-                    info_only: false,
                     add_daymarker: true,
                 },
             )