Revert "Re-export core::ffi types from std::ffi"

This reverts commit 9aed829fe6.

Fixes https://github.com/rust-lang/rust/issues/96435 , a regression
in crates doing `use std::ffi::*;` and `use std::os::raw::*;`.

We can re-add this re-export once the `core::ffi` types
are stable, and thus the `std::os::raw` types can become re-exports as
well, which will avoid the conflict. (Type aliases to the same type
still conflict, but re-exports of the same type don't.)

library/std/src/ffi/mod.rs

@@ -171,15 +171,6 @@ pub use self::os_str::{OsStr, OsString};
 #[stable(feature = "core_c_void", since = "1.30.0")]
 pub use core::ffi::c_void;
 
-#[unstable(feature = "core_ffi_c", issue = "94501")]
-pub use core::ffi::{
-    c_char, c_double, c_float, c_int, c_long, c_longlong, c_schar, c_short, c_uchar, c_uint,
-    c_ulong, c_ulonglong, c_ushort,
-};
-
-#[unstable(feature = "c_size_t", issue = "88345")]
-pub use core::ffi::{c_ptrdiff_t, c_size_t, c_ssize_t};
-
 #[unstable(
     feature = "c_variadic",
     reason = "the `c_variadic` feature has not been properly tested on \

library/std/src/lib.rs

@@ -307,7 +307,6 @@
 // Only for re-exporting:
 #![feature(assert_matches)]
 #![feature(async_iterator)]
-#![feature(c_size_t)]
 #![feature(c_variadic)]
 #![feature(cfg_accessible)]
 #![feature(cfg_eval)]