Rollup merge of rust-lang#153534 - Zalathar:flaky-stress, r=Mark-Simulacrum

Remove a flaky `got_timeout` assert from two channel tests

In CI, the receiver thread can be descheduled for a surprisingly long time, so there's no guarantee that a timeout actually occurs.

One of these tests actually failed in rust-lang#153387 (comment).

Earlier failures:
- rust-lang#150365 (comment)
- rust-lang#147775 (comment)

---

- Prior art: rust-lang#152878

Author: JonathanBrouwer

library/std/tests/sync/mpmc.rs

@@ -475,23 +475,20 @@ fn stress_recv_timeout_two_threads() {
     });
 
     let mut recv_count = 0;
-    let mut got_timeout = false;
     loop {
         match rx.recv_timeout(timeout) {
             Ok(n) => {
                 assert_eq!(n, 1usize);
                 recv_count += 1;
             }
             Err(RecvTimeoutError::Timeout) => {
-                got_timeout = true;
                 continue;
             }
             Err(RecvTimeoutError::Disconnected) => break,
         }
     }
 
     assert_eq!(recv_count, stress);
-    assert!(got_timeout);
 }
 
 #[test]

library/std/tests/sync/mpsc.rs

@@ -438,23 +438,20 @@ fn stress_recv_timeout_two_threads() {
     });
 
     let mut recv_count = 0;
-    let mut got_timeout = false;
     loop {
         match rx.recv_timeout(timeout) {
             Ok(n) => {
                 assert_eq!(n, 1usize);
                 recv_count += 1;
             }
             Err(RecvTimeoutError::Timeout) => {
-                got_timeout = true;
                 continue;
             }
             Err(RecvTimeoutError::Disconnected) => break,
         }
     }
 
     assert_eq!(recv_count, stress);
-    assert!(got_timeout);
 }
 
 #[test]