Fix dropping issues with StaticVec and use it everywhere.

src/module.rs

@@ -716,7 +716,7 @@ impl Module {
 ///
 /// A `StaticVec` is used because most module-level access contains only one level,
 /// and it is wasteful to always allocate a `Vec` with one element.
-#[derive(Clone, Eq, PartialEq, Hash, Default)]
+#[derive(Clone, Eq, PartialEq, Default)]
 pub struct ModuleRef(StaticVec<(String, Position)>, Option<NonZeroUsize>);
 
 impl fmt::Debug for ModuleRef {