Remove assertion from oneshot_multi_thread_send_close_stress
Remove assertion from oneshot_multi_thread_send_close_stress

There was a race condition between dropping the channel and sending the value. The sending was changed to ignore the result.

crossbeam-rs/crossbeam,crossbeam-rs/crossbeam,crossbeam-rs/crossbeam,crossbeam-rs/crossbeam,aturon/crossbeam