Add some initial deny for unused_imports and unused_variables

Additional unused variable fix on unix

Remove unused import on unix

Remove unused windows import

lib/win-exception-handler/src/exception_handling.rs

@@ -1,4 +1,3 @@
-use std::ffi::c_void;
 use std::ptr::NonNull;
 use wasmer_runtime_core::vm::{Ctx, Func};
 

lib/win-exception-handler/src/lib.rs

@@ -1,3 +1,5 @@
+#![deny(unused_imports, unused_variables)]
+
 #[cfg(windows)]
 mod exception_handling;