Remove unused reponse field

Author: crossle

library/src/main/kotlin/one/mixin/bot/api/MixinResponse.kt

@@ -23,10 +23,4 @@ class MixinResponse<T>() {
 
     val isSuccess: Boolean
         get() = error == null
-
-    val errorCode: Int
-        get() = if (error != null) error!!.code else 0
-
-    val errorDescription: String
-        get() = if (error != null) error!!.description else ""
 }