Remove unnecessary From<Error> for io::Error in no_std mode

src/error.rs

@@ -129,6 +129,7 @@ pub enum Category {
     Eof,
 }
 
+#[cfg(feature = "std")]
 #[cfg_attr(feature = "cargo-clippy", allow(fallible_impl_from))]
 impl From<Error> for io::Error {
     /// Convert a `serde_json::Error` into an `io::Error`.

src/io/core.rs

@@ -4,10 +4,8 @@
 use lib::*;
 
 pub enum ErrorKind {
-    InvalidData,
     WriteZero,
     Other,
-    UnexpectedEof,
 }
 
 pub struct Error {