Remove redundant import

[taiki-e]

error: the item `Future` is imported redundantly
  --> tests/rwlock.rs:11:5
   |
9  | use futures_lite::prelude::*;
   |     ------------------------ the item `Future` is already imported here
10 | #[cfg(not(target_family = "wasm"))]
11 | use std::future::Future;
   |     ^^^^^^^^^^^^^^^^^^^
   |
   = note: `-D unused-imports` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(unused_imports)]`

[taiki-e]

Oh, miri reports deadlock...

https://github.com/smol-rs/async-lock/actions/runs/8130186743/job/22218147586?pr=80

error: deadlock: the evaluated program deadlocked
  --> /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/pal/unix/futex.rs:70:21
   |
70 |                     )
   |                     ^ the evaluated program deadlocked
   |
   = note: inside `std::sys::pal::unix::futex::futex_wait` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/pal/unix/futex.rs:70:21: 70:22
   = note: inside `std::sys::locks::condvar::futex::Condvar::wait_optional_timeout` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/locks/condvar/futex.rs:49:17: 49:62
   = note: inside `std::sys::locks::condvar::futex::Condvar::wait` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/locks/condvar/futex.rs:33:9: 33:48
   = note: inside `std::sync::Condvar::wait::<()>` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sync/condvar.rs:189:13: 189:34
   = note: inside `parking::Inner::park` at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/parking-2.2.0/src/lib.rs:366:25: 366:42
   = note: inside `parking::Parker::park` at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/parking-2.2.0/src/lib.rs:121:9: 121:39
   = note: inside closure at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/futures-lite-2.2.0/src/future.rs:101:34: 101:47
   = note: inside `std::thread::LocalKey::<std::cell::RefCell<(parking::Parker, std::task::Waker)>>::try_with::<{closure@futures_lite::future::block_on<(), {async block@tests/barrier.rs:22:38: 25:22}>::{closure#0}}, ()>` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/local.rs:284:16: 284:31
   = note: inside `std::thread::LocalKey::<std::cell::RefCell<(parking::Parker, std::task::Waker)>>::with::<{closure@futures_lite::future::block_on<(), {async block@tests/barrier.rs:22:38: 25:22}>::{closure#0}}, ()>` at /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/local.rs:2[60](https://github.com/smol-rs/async-lock/actions/runs/8130186743/job/22218147586?pr=80#step:4:61):9: 260:25
   = note: inside `futures_lite::future::block_on::<(), {async block@tests/barrier.rs:22:38: 25:22}>` at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/futures-lite-2.2.0/src/future.rs:78:5: 104:7
note: inside closure
  --> tests/barrier.rs:22:21
   |
22 | /                     future::block_on(async move {
23 | |                         let res = c.wait().await;
24 | |                         tx.send(res.is_leader()).await.unwrap();
25 | |                     })
   | |______________________^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to 1 previous error