Remove usage of deprecated std::error::Error methods (#1206) (#1245)

tokio-executor/src/enter.rs

@@ -22,7 +22,7 @@ pub struct EnterError {
 impl fmt::Debug for EnterError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("EnterError")
-            .field("reason", &self.description())
+            .field("reason", &format!("{}", self))
             .finish()
     }
 }

tokio-executor/src/error.rs

@@ -39,12 +39,11 @@ impl SpawnError {
 
 impl fmt::Display for SpawnError {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(fmt, "{}", self.description())
+        write!(
+            fmt,
+            "attempted to spawn task while the executor is at capacity or shut down"
+        )
     }
 }
 
-impl Error for SpawnError {
-    fn description(&self) -> &str {
-        "attempted to spawn task while the executor is at capacity or shut down"
-    }
-}
+impl Error for SpawnError {}