[wasi-common]: winx now returns io::Error directly (#1243)

* Winx now returns io::Error

This commit is a spiritual follower of #1242 in the sense that it
adjusts `winx` to also return `io::Error` directly rather than
tossing a custom error type here and there.

* Adapt wasi-common to changes in winx

* Run cargo fmt

* Swap overly big map_err with explicit match

crates/wasi-common/winx/src/lib.rs

@@ -24,8 +24,3 @@
 pub mod file;
 mod ntdll;
 pub mod time;
-pub mod winerror;
-
-use winerror::WinError;
-
-pub type Result<T> = std::result::Result<T, WinError>;