docs(rust): remove outdated documentation about userparser
Remove documentation for type `UserParser` that was removed in
@@ -12,9 +12,6 @@ use ockam_core::Decodable;
/// A parser for a protocol fragment
///
-/// **If you are not a protocol author, you may want to use
-/// [`UserParser`](UserParser) instead!**
-///
/// Protocols are implemented as separate structures, wrapped in a
/// carrier type. Because Rust can't have a function return different
/// types from a function, each protocol message (here called
