Rollup merge of rust-lang#114965 - benschulz:mpsc-drop, r=dtolnay

Remove Drop impl of mpsc Receiver and (Sync)Sender

This change removes the empty `Drop` implementations for `mpsc::Receiver`, `mpsc::Sender` and `mpsc::SyncSender`. These implementations do not specify `#[may_dangle]`, so by removing them we make `mpsc` types play nice with drop check.

This was previously attempted in [rust-lang#105243](rust-lang#105243 (comment)) but then [abandoned due to a test failure](rust-lang#105243 (comment)). I've aligned the test with those for `Mutex` and `RwLock`.

Author: Dylan-DPC

std/src/sync/mpsc/mod.rs

@@ -626,11 +626,6 @@ impl<T> Clone for Sender<T> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for Sender<T> {
-    fn drop(&mut self) {}
-}
-
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Sender<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -755,11 +750,6 @@ impl<T> Clone for SyncSender<T> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for SyncSender<T> {
-    fn drop(&mut self) {}
-}
-
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for SyncSender<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -1096,11 +1086,6 @@ impl<T> IntoIterator for Receiver<T> {
     }
 }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for Receiver<T> {
-    fn drop(&mut self) {}
-}
-
 #[stable(feature = "mpsc_debug", since = "1.8.0")]
 impl<T> fmt::Debug for Receiver<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {