Ban do_send_async and do_send functions

Both of these discard the return value which can lead to hard to find
bugs if the return value is an `Err`.

clippy.toml

@@ -0,0 +1,4 @@
+disallowed-methods = [
+  "xtra::Address::do_send_async", # discards the return value, possibly swallowing an error
+  "xtra::Address::do_send", # discards the return value, possibly swallowing an error
+]

daemon/src/lib.rs

@@ -1,4 +1,6 @@
 #![cfg_attr(not(test), warn(clippy::unwrap_used))]
+#![warn(clippy::disallowed_method)]
+
 use crate::db::load_all_cfds;
 use crate::maker_cfd::{FromTaker, NewTakerOnline};
 use crate::model::cfd::{Cfd, Order, UpdateCfdProposals};

daemon/src/maker_cfd.rs

@@ -329,6 +329,9 @@ where
             None => None,
         };
 
+        // Need to use `do_send_async` here because we are being invoked from the
+        // `maker_inc_connections::Actor`. Using `send` would result in a deadlock.
+        #[allow(clippy::disallowed_method)]
         self.takers
             .do_send_async(maker_inc_connections::TakerMessage {
                 taker_id,