Cygwin: pty: Remove destructor for fhandler_pty_master class.

- The destructor for fhandler_pty_master class does not seem to be
  necessary anymore. Therefore, it has been removed.

winsup/cygwin/fhandler.h

@@ -2218,7 +2218,6 @@ public:
   HANDLE get_echo_handle () const { return echo_r; }
   /* Constructor */
   fhandler_pty_master (int);
-  ~fhandler_pty_master ();
 
   DWORD pty_master_thread ();
   DWORD pty_master_fwd_thread ();

winsup/cygwin/fhandler_tty.cc

@@ -2126,15 +2126,6 @@ fhandler_pty_master::fhandler_pty_master (int unit)
   set_name ("/dev/ptmx");
 }
 
-fhandler_pty_master::~fhandler_pty_master ()
-{
-  /* Without this wait, helper process for pseudo console
-     sometimes remains running after the pty session is
-     closed. The reason is not clear. */
-  if (to_master && from_master)
-    Sleep (20);
-}
-
 int
 fhandler_pty_master::open (int flags, mode_t)
 {