Add deny dead_code lint and fix one error

lib/middleware-common/src/lib.rs

@@ -1,4 +1,9 @@
-#![deny(unused_imports, unused_variables, unused_unsafe, unreachable_patterns)]
-
+#![deny(
+    dead_code,
+    unused_imports,
+    unused_variables,
+    unused_unsafe,
+    unreachable_patterns
+)]
 pub mod call_trace;
 pub mod metering;