Resolve clippy::unnecessary_mut_passed

    error: the method `validate_lock_acquire` doesn't need a mutable reference
       --> src/sync.rs:477:49
        |
    477 |                 data_race.validate_lock_acquire(&mut condvar.data_race, waiter.thread);
        |                                                 ^^^^^^^^^^^^^^^^^^^^^^
        |
        = note: `-D clippy::unnecessary-mut-passed` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_mut_passed

Author: dtolnay

src/lib.rs

@@ -21,7 +21,6 @@
     clippy::needless_lifetimes,
     clippy::new_without_default,
     clippy::single_match,
-    clippy::unnecessary_mut_passed,
     clippy::useless_conversion,
     clippy::useless_format
 )]

src/sync.rs

@@ -474,7 +474,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         }
         condvar.waiters.pop_front().map(|waiter| {
             if let Some(data_race) = data_race {
-                data_race.validate_lock_acquire(&mut condvar.data_race, waiter.thread);
+                data_race.validate_lock_acquire(&condvar.data_race, waiter.thread);
             }
             (waiter.thread, waiter.mutex)
         })