Rollup merge of rust-lang#93134 - tlyu:delete-stdin-split, r=Amanieu

delete `Stdin::split` forwarder

Part of rust-lang#87096. Delete the `Stdin::split` forwarder because it's seen as too niche to expose at this level.

`@rustbot` label T-libs-api A-io

library/std/src/io/stdio.rs

@@ -7,7 +7,7 @@ use crate::io::prelude::*;
 
 use crate::cell::{Cell, RefCell};
 use crate::fmt;
-use crate::io::{self, BufReader, IoSlice, IoSliceMut, LineWriter, Lines, Split};
+use crate::io::{self, BufReader, IoSlice, IoSliceMut, LineWriter, Lines};
 use crate::lazy::SyncOnceCell;
 use crate::pin::Pin;
 use crate::sync::atomic::{AtomicBool, Ordering};
@@ -465,29 +465,6 @@ impl Stdin {
     pub fn lines(self) -> Lines<StdinLock<'static>> {
         self.into_locked().lines()
     }
-
-    /// Consumes this handle and returns an iterator over input bytes,
-    /// split at the specified byte value.
-    ///
-    /// For detailed semantics of this method, see the documentation on
-    /// [`BufRead::split`].
-    ///
-    /// # Examples
-    ///
-    /// ```no_run
-    /// #![feature(stdin_forwarders)]
-    /// use std::io;
-    ///
-    /// let splits = io::stdin().split(b'-');
-    /// for split in splits {
-    ///     println!("got a chunk: {}", String::from_utf8_lossy(&split.unwrap()));
-    /// }
-    /// ```
-    #[must_use = "`self` will be dropped if the result is not used"]
-    #[unstable(feature = "stdin_forwarders", issue = "87096")]
-    pub fn split(self, byte: u8) -> Split<StdinLock<'static>> {
-        self.into_locked().split(byte)
-    }
 }
 
 #[stable(feature = "std_debug", since = "1.16.0")]