Remove support for calling getrandom(), we now always call getentropy()

Only Linux and FreeBSD provide getrandom(), but they both also provide
getentropy() since the same version and we already tried to call that.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
GH: #6405

crypto/rand/rand_unix.c

@@ -164,20 +164,6 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 #   error "Seeding uses urandom but DEVRANDOM is not configured"
 #  endif
 
-#  if defined(__GLIBC__) && defined(__GLIBC_PREREQ)
-#   if __GLIBC_PREREQ(2, 25)
-#    define OPENSSL_HAVE_GETRANDOM
-#   endif
-#  endif
-
-#  if (defined(__FreeBSD__) && __FreeBSD_version >= 1200061)
-#   define OPENSSL_HAVE_GETRANDOM
-#  endif
-
-#  if defined(OPENSSL_HAVE_GETRANDOM)
-#   include <sys/random.h>
-#  endif
-
 #  if defined(OPENSSL_RAND_SEED_OS)
 #   if !defined(DEVRANDOM)
 #    error "OS seeding requires DEVRANDOM to be configured"
@@ -265,10 +251,6 @@ int syscall_random(void *buf, size_t buflen)
     if (p_getentropy.p != NULL)
         return p_getentropy.f(buf, buflen);
 
-#  if defined(OPENSSL_HAVE_GETRANDOM)
-    return (int)getrandom(buf, buflen, 0);
-#  endif
-
     /* Linux supports this since version 3.17 */
 #  if defined(__linux) && defined(SYS_getrandom)
     return (int)syscall(SYS_getrandom, buf, buflen, 0);