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.

src/test_utils.rs

@@ -1104,7 +1104,6 @@ ORDER BY id"
             self,
             chat_id,
             MessageListOptions {
-                info_only: false,
                 add_daymarker: false,
             },
         )