fix clippy

Author: loongs-zhang

core/src/coroutine/korosensei.rs

@@ -7,8 +7,6 @@ use crate::{catch, warn};
 use corosensei::stack::{DefaultStack, Stack};
 use corosensei::trap::TrapHandlerRegs;
 use corosensei::CoroutineResult;
-#[cfg(all(any(target_os = "linux", target_os = "android"), target_arch = "x86"))]
-use num_conv::CastSigned;
 use std::cell::{Cell, RefCell, UnsafeCell};
 use std::collections::VecDeque;
 use std::ffi::c_longlong;