Remove implementation of deprecated Error::description function

Author: eldruin

src/error.rs

@@ -22,13 +22,6 @@ pub enum Error {
 }
 
 impl ::std::error::Error for Error {
-    fn description(&self) -> &str {
-        match *self {
-            Error::Io(ref e) => e.description(),
-            Error::Unexpected(_) => "something unexpected",
-        }
-    }
-
     fn cause(&self) -> Option<&dyn (::std::error::Error)> {
         match *self {
             Error::Io(ref e) => Some(e),