Remove Clone and PartialEq impls from error type

These are not widely provided for error types in the ecosystem.

Author: dtolnay

_src/error-handling.md

@@ -53,7 +53,7 @@ pub type Result<T> = std::result::Result<T, Error>;
 // information in its error type, for example the line and column at which the
 // error occurred, the byte offset into the input, or the current key being
 // processed.
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Debug)]
 pub enum Error {
     // One or more variants that can be created by data structures through the
     // `ser::Error` and `de::Error` traits. For example the Serialize impl for