Remove some #[allow(warnings)] (#376)

These were probably added during development and then forgotten to be
removed.

src/extract/path/mod.rs

@@ -150,7 +150,6 @@ where
 {
     type Rejection = PathParamsRejection;
 
-    #[allow(warnings)]
     async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
         let params = match req
             .extensions_mut()