Remove OpenBSD change

Author: vstinner

configure

@@ -7563,7 +7563,6 @@ case "$ac_sys_system" in
   Darwin) _PYTHREAD_NAME_MAXLEN=63;;
   iOS) _PYTHREAD_NAME_MAXLEN=63;;
   FreeBSD*) _PYTHREAD_NAME_MAXLEN=19;; # gh-131268
-  OpenBSD*) _PYTHREAD_NAME_MAXLEN=23;; # gh-131268
   *) _PYTHREAD_NAME_MAXLEN=;;
 esac
 if test -n "$_PYTHREAD_NAME_MAXLEN"; then