docs: fix stdin documentation (#6581)

The code for `output` indicates that only sets `stdout` and `stderr`, 
yet the docs for `stdin` indicated that it too would be set. This seems 
like it was just a simple copy/paste typo, so correct `stdin` to note
that it just defaults to `inherit`.

Fixes #6577.

tokio/src/process/mod.rs

@@ -544,11 +544,9 @@ impl Command {
 
     /// Sets configuration for the child process's standard input (stdin) handle.
     ///
-    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
-    /// defaults to [`piped`] when used with `output`.
+    /// Defaults to [`inherit`].
     ///
     /// [`inherit`]: std::process::Stdio::inherit
-    /// [`piped`]: std::process::Stdio::piped
     ///
     /// # Examples
     ///