Remove Message impl for ManuallyDrop

This was added in error, really, there is no case where we would want `T: Message` to include `ManuallyDrop<T>` - that would simply only serve to confuse the user, as they might think the `dealloc` method wouldn't be called for `Id<ManuallyDrop<MyObject>, O>`, which it definitely would!

Author: madsmtm

objc2/CHANGELOG.md

@@ -66,6 +66,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * Properly sealed the `MessageArguments` trait (it already had a hidden
   method, so this is not really a breaking change).
 
+### Removed
+* **BREAKING**: `ManuallyDrop` no longer implements `Message` directly.
+
 
 ## 0.3.0-alpha.6 - 2022-01-03
 

objc2/src/message/mod.rs

@@ -61,9 +61,6 @@ use self::verify::{verify_message_signature, VerificationError};
 /// [`objc_msgSend`]: https://developer.apple.com/documentation/objectivec/1456712-objc_msgsend
 pub unsafe trait Message: RefEncode {}
 
-// SAFETY: `ManuallyDrop` is `repr(transparent)`.
-unsafe impl<T: Message + ?Sized> Message for ManuallyDrop<T> {}
-
 unsafe impl Message for Object {}
 
 // TODO: Make this fully private