pipe: Remove unnecessary miri exclusions from no_run code

Author: tbu-

library/std/src/io/pipe.rs

@@ -33,11 +33,9 @@ use crate::sys::anonymous_pipe::{AnonPipe, pipe as pipe_inner};
 ///
 /// ```no_run
 /// #![feature(anonymous_pipe)]
-/// # #[cfg(miri)] fn main() {}
-/// # #[cfg(not(miri))]
-/// # fn main() -> std::io::Result<()> {
 /// use std::process::Command;
 /// use std::io::{pipe, Read, Write};
+///
 /// let (ping_rx, mut ping_tx) = pipe()?;
 /// let (mut pong_rx, pong_tx) = pipe()?;
 ///
@@ -55,7 +53,6 @@ use crate::sys::anonymous_pipe::{AnonPipe, pipe as pipe_inner};
 ///
 /// echo_server.wait()?;
 /// # Ok(())
-/// # }
 /// ```
 /// [changes]: io#platform-specific-behavior
 /// [man page]: https://man7.org/linux/man-pages/man7/pipe.7.html
@@ -82,12 +79,10 @@ impl PipeReader {
     ///
     /// ```no_run
     /// #![feature(anonymous_pipe)]
-    /// # #[cfg(miri)] fn main() {}
-    /// # #[cfg(not(miri))]
-    /// # fn main() -> std::io::Result<()> {
     /// use std::fs;
     /// use std::io::{pipe, Write};
     /// use std::process::Command;
+    ///
     /// const NUM_SLOT: u8 = 2;
     /// const NUM_PROC: u8 = 5;
     /// const OUTPUT: &str = "work.txt";
@@ -127,7 +122,6 @@ impl PipeReader {
     /// fs::remove_file(OUTPUT)?;
     /// assert_eq!(xs, "x".repeat(NUM_PROC.into()));
     /// # Ok(())
-    /// # }
     /// ```
     #[unstable(feature = "anonymous_pipe", issue = "127154")]
     pub fn try_clone(&self) -> io::Result<Self> {
@@ -142,11 +136,9 @@ impl PipeWriter {
     ///
     /// ```no_run
     /// #![feature(anonymous_pipe)]
-    /// # #[cfg(miri)] fn main() {}
-    /// # #[cfg(not(miri))]
-    /// # fn main() -> std::io::Result<()> {
     /// use std::process::Command;
     /// use std::io::{pipe, Read};
+    ///
     /// let (mut reader, writer) = pipe()?;
     ///
     /// // Spawn a process that writes to stdout and stderr.
@@ -167,7 +159,6 @@ impl PipeWriter {
     ///
     /// peer.wait()?;
     /// # Ok(())
-    /// # }
     /// ```
     #[unstable(feature = "anonymous_pipe", issue = "127154")]
     pub fn try_clone(&self) -> io::Result<Self> {