Revert "tests: alter integration tests for stdio to not use a handrolled cat implementation (#4803)" (#4854)

This reverts commit d8cad13fd9.

tests-integration/src/bin/test-cat.rs

@@ -1,14 +1,20 @@
 //! A cat-like utility that can be used as a subprocess to test I/O
 //! stream communication.
 
-use tokio::io::AsyncWriteExt;
+use std::io;
+use std::io::Write;
 
-#[tokio::main(flavor = "current_thread")]
-async fn main() {
-    let mut stdin = tokio::io::stdin();
-    let mut stdout = tokio::io::stdout();
-
-    tokio::io::copy(&mut stdin, &mut stdout).await.unwrap();
-
-    stdout.flush().await.unwrap();
+fn main() {
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
+    let mut line = String::new();
+    loop {
+        line.clear();
+        stdin.read_line(&mut line).unwrap();
+        if line.is_empty() {
+            break;
+        }
+        stdout.write_all(line.as_bytes()).unwrap();
+    }
+    stdout.flush().unwrap();
 }