Auto merge of #25187 - alexcrichton:mem-forget-safe, r=brson

This commit is an implementation of [RFC 1066][rfc] where the conclusion was
that leaking a value is a safe operation in Rust code, so updating the signature
of this function follows suit.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1066-safe-mem-forget.md

Closes #25186

src/libstd/sys/unix/fd.rs

@@ -31,7 +31,7 @@ impl FileDesc {
     /// Extracts the actual filedescriptor without closing it.
     pub fn into_raw(self) -> c_int {
         let fd = self.fd;
-        unsafe { mem::forget(self) };
+        mem::forget(self);
         fd
     }
 

src/libstd/sys/windows/handle.rs

@@ -32,7 +32,7 @@ impl Handle {
 
     pub fn into_raw(self) -> HANDLE {
         let ret = self.0;
-        unsafe { mem::forget(self) }
+        mem::forget(self);
         return ret;
     }