add missing _ctypes functions (#13067)

stdlib/@tests/stubtest_allowlists/darwin.txt

@@ -24,11 +24,6 @@ select.POLLMSG   # system dependent
 (posix.ST_[A-Z]+)?
 (termios.[A-Z0-9_]+)?
 
-# Exists at runtime, but missing from stubs
-_ctypes.dlclose
-_ctypes.dlopen
-_ctypes.dlsym
-
 # ==========
 # Allowlist entries that cannot or should not be fixed
 # ==========

stdlib/@tests/stubtest_allowlists/linux.txt

@@ -5,10 +5,6 @@
 curses.has_key
 selectors.KqueueSelector
 
-_ctypes.dlclose
-_ctypes.dlopen
-_ctypes.dlsym
-
 # ==========
 # Allowlist entries that cannot or should not be fixed
 # ==========