roll back the unsound borrowing API

src/sys/tskbox.rs

@@ -2,8 +2,7 @@ use std::ptr::NonNull;
 
 pub struct TskBox<T> {
     tsk: NonNull<T>,
-    teardown: Option<unsafe extern "C" fn(*mut T) -> i32>,
-    owning: bool,
+    teardown: unsafe extern "C" fn(*mut T) -> i32,
 }
 
 impl<T> TskBox<T> {
@@ -14,11 +13,7 @@ impl<T> TskBox<T> {
         let x = unsafe { libc::malloc(std::mem::size_of::<T>()) as *mut T };
         let _ = init(x);
         let tsk = NonNull::new(x).unwrap();
-        Self {
-            tsk,
-            teardown: Some(teardown),
-            owning: true,
-        }
+        Self { tsk, teardown }
     }
 
     pub fn as_ref(&self) -> &T {
@@ -40,14 +35,10 @@ impl<T> TskBox<T> {
 
 impl<T> Drop for TskBox<T> {
     fn drop(&mut self) {
-        if let Some(teardown) = self.teardown {
-            unsafe {
-                (teardown)(self.tsk.as_mut() as *mut T);
-            }
-        }
-        if self.owning {
-            unsafe { libc::free(self.tsk.as_ptr() as *mut libc::c_void) }
+        unsafe {
+            (self.teardown)(self.tsk.as_mut() as *mut T);
         }
+        unsafe { libc::free(self.tsk.as_ptr() as *mut libc::c_void) }
     }
 }
 
@@ -70,7 +61,7 @@ fn test_miri() {
 
     let options = 0_i32;
 
-    let b = TskBox::new(
+    let _ = TskBox::new(
         |x: *mut X| unsafe {
             (*x).data = options;
             0
@@ -93,7 +84,7 @@ fn test_table_collection_tskbox() {
 #[test]
 fn test_table_collection_tskbox_shared_ptr() {
     let flags: u32 = 0;
-    let tables = TskBox::new(
+    let _ = TskBox::new(
         |t: *mut super::bindings::tsk_table_collection_t| unsafe {
             super::bindings::tsk_table_collection_init(t, flags)
         },