Rollup merge of #135491 - RalfJung:remove-dead-rustc_allowed_through_…

…unstable_modules, r=Mark-Simulacrum

Remove dead rustc_allowed_through_unstable_modules for std::os::fd contents

As far as I was able to reconstruct, the history here is roughly as follows:
- #99723 added some `rustc_allowed_through_unstable_modules` to the types in `std::os::fd::raw` since they were accessible on stable via the unstable `std::os::wasi::io::AsRawFd` path. (This was needed to fix #99502.)
- Shortly thereafter, #98368 re-organized things so that instead of re-exporting from an internal  `std::os::wasi::io::raw`,   `std::os::wasi::io::AsRawFd` is now directly re-exported from `std::os::fd`. This also made `library/std/src/os/wasi/io/raw.rs` entirely dead code as far as I can tell, it's not imported by anything any more.
- Shortly thereafter, #103308 stabilizes `std::os::wasi::io`, so `rustc_allowed_through_unstable_modules` is not needed any more to access `std::os::wasi::io::AsRawFd`. There is even a comment in `library/std/src/os/wasi/io/raw.rs` saying the attribute can be removed now, but that file is dead code so it is not touched as part of the stabilization.

I did a grep for `pub use crate::os::fd` and all the re-exports I could find are in stable modules. So given all that, we can remove the  `rustc_allowed_through_unstable_modules` (hoping they are not also re-exported somewhere else, it's really hard to be sure about this).

I have checked that std still builds after this PR on the wasm32-wasip2 target.

library/std/src/os/fd/raw.rs

@@ -19,11 +19,9 @@ use crate::sys_common::{AsInner, IntoInner};
 use crate::{fs, io};
 
 /// Raw file descriptors.
-#[rustc_allowed_through_unstable_modules]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg(not(target_os = "hermit"))]
 pub type RawFd = raw::c_int;
-#[rustc_allowed_through_unstable_modules]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg(target_os = "hermit")]
 pub type RawFd = i32;
@@ -33,7 +31,6 @@ pub type RawFd = i32;
 /// This is only available on unix and WASI platforms and must be imported in
 /// order to call the method. Windows platforms have a corresponding
 /// `AsRawHandle` and `AsRawSocket` set of traits.
-#[rustc_allowed_through_unstable_modules]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait AsRawFd {
     /// Extracts the raw file descriptor.
@@ -67,7 +64,6 @@ pub trait AsRawFd {
 
 /// A trait to express the ability to construct an object from a raw file
 /// descriptor.
-#[rustc_allowed_through_unstable_modules]
 #[stable(feature = "from_raw_os", since = "1.1.0")]
 pub trait FromRawFd {
     /// Constructs a new instance of `Self` from the given raw file
@@ -112,7 +108,6 @@ pub trait FromRawFd {
 
 /// A trait to express the ability to consume an object and acquire ownership of
 /// its raw file descriptor.
-#[rustc_allowed_through_unstable_modules]
 #[stable(feature = "into_raw_os", since = "1.4.0")]
 pub trait IntoRawFd {
     /// Consumes this object, returning the raw underlying file descriptor.

library/std/src/os/wasi/io/mod.rs

@@ -4,3 +4,7 @@
 
 #[stable(feature = "io_safety_wasi", since = "1.65.0")]
 pub use crate::os::fd::*;
+
+// Tests for this module
+#[cfg(test)]
+mod tests;