[rust] Add "unsafe" to the testing-mode tor_malloc_ wrapper.

This change lets us remove the allow(unused_unsafe) directive
from allocate_and_copy_string().

src/rust/tor_allocate/tor_allocate.rs

@@ -12,9 +12,9 @@ extern "C" {
 // Defined only for tests, used for testing purposes, so that we don't need
 // to link to tor C files. Uses the system allocator
 #[cfg(test)]
-extern "C" fn tor_malloc_(size: usize) -> *mut c_void {
+unsafe extern "C" fn tor_malloc_(size: usize) -> *mut c_void {
     use libc::malloc;
-    unsafe { malloc(size) }
+    malloc(size)
 }
 
 /// Allocate memory using tor_malloc_ and copy an existing string into the
@@ -28,10 +28,6 @@ extern "C" fn tor_malloc_(size: usize) -> *mut c_void {
 ///
 /// A `*mut c_char` that should be freed by tor_free in C
 ///
-/// Allow unused unsafe as at compile-time, we get warnings that unsafe is not
-/// needed even though this calls tor_malloc in C.
-///
-#[allow(unused_unsafe)]
 pub fn allocate_and_copy_string(src: &String) -> *mut c_char {
     let bytes: &[u8] = src.as_bytes();