Remove peek() call, not in 3.15.

Author: nascheme

Lib/test/test_free_threading/test_io.py

@@ -138,7 +138,6 @@ def reader():
                 shared.seek(0)
                 shared.read()
                 shared.seek(0)
-                shared.peek()
                 shared.getvalue()
 
         threads = [threading.Thread(target=writer) for _ in range(writers)]