random_r: Remove support for OSF/1. * lib/stdlib.in.h: Don't include <random.h>. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Don't initialize HAVE_RANDOM_H. * m4/random_r.m4 (gl_FUNC_RANDOM_R): Don't set HAVE_RANDOM_H. Don't set REPLACE_RANDOM_R on OSF/1. * modules/stdlib-h (Makefile.am): Don't substitute HAVE_RANDOM_H.