Remove the obsolete MAXFD constant and Popen._close_fds() method.

They should have been removed years ago when removing the old pure
Python implementation from the file.

Lib/subprocess.py

@@ -469,10 +469,6 @@ def __repr__(self):
         __del__ = Close
         __str__ = __repr__
 
-try:
-    MAXFD = os.sysconf("SC_OPEN_MAX")
-except:
-    MAXFD = 256
 
 # This lists holds Popen instances for which the underlying process had not
 # exited at the time its __del__ method got called: those processes are wait()ed
@@ -1335,16 +1331,6 @@ def _get_handles(self, stdin, stdout, stderr):
                     errread, errwrite)
 
 
-        def _close_fds(self, fds_to_keep):
-            start_fd = 3
-            for fd in sorted(fds_to_keep):
-                if fd >= start_fd:
-                    os.closerange(start_fd, fd)
-                    start_fd = fd + 1
-            if start_fd <= MAXFD:
-                os.closerange(start_fd, MAXFD)
-
-
         def _execute_child(self, args, executable, preexec_fn, close_fds,
                            pass_fds, cwd, env,
                            startupinfo, creationflags, shell,