Fix double import in wasm thread

The `unsupported` type is imported two times, as `super::unsupported` and as `crate::sys::unsupported`, throwing an error. Remove `super::unsupported` in favor of the other.

Author: tversteeg

library/std/src/sys/wasm/atomics/thread.rs

@@ -1,4 +1,3 @@
-use super::unsupported;
 use crate::ffi::CStr;
 use crate::io;
 use crate::num::NonZeroUsize;