test: remove flaky test (#5468)

tests/lean/Process.lean

@@ -19,12 +19,6 @@ def usingIO {α} (x : IO α) : IO α := x
   discard $ child.wait;
   child.stdout.readToEnd
 
-#eval usingIO do
-  let child ← spawn { cmd := "true", stdin := Stdio.piped };
-  discard $ child.wait;
-  child.stdin.putStrLn "ha!";
-  child.stdin.flush <|> IO.println "flush of broken pipe failed"
-
 #eval usingIO do
   -- produce enough output to fill both pipes on all platforms
   let out ← output { cmd := "sh", args := #["-c", "printf '%100000s' >& 2; printf '%100001s'"] };

tests/lean/Process.lean.expected.out

@@ -2,7 +2,6 @@
 0
 "ho!\n"
 "hu!\n"
-flush of broken pipe failed
 100001
 100000
 0