Remove deprecated API

parser/Cargo.toml

@@ -8,6 +8,7 @@ license = "MIT/Apache-2.0"
 description = "The missing YAML 1.2 parser for rust"
 repository = "https://github.com/chyh1990/yaml-rust"
 readme = "README.md"
+edition = "2018"
 
 [dependencies]
 linked-hash-map = ">=0.0.9, <0.6"

parser/src/emitter.rs

@@ -10,13 +10,6 @@ pub enum EmitError {
 }
 
 impl Error for EmitError {
-    fn description(&self) -> &str {
-        match *self {
-            EmitError::FmtError(ref err) => err.description(),
-            EmitError::BadHashmapKey => "bad hashmap key",
-        }
-    }
-
     fn cause(&self) -> Option<&dyn Error> {
         None
     }