Remove explicit check for gnutls_rnd

Introduced in gnutls 2.12, but we require gnutls >= 3.2
Check added by commit <2d23d145>.
Signed-off-by: NJán Tomko <jtomko@redhat.com>

m4/virt-gnutls.m4

@@ -37,7 +37,6 @@ AC_DEFUN([LIBVIRT_CHECK_GNUTLS],[
       #include <gnutls/gnutls.h>
     ]])
 
-    AC_CHECK_FUNCS([gnutls_rnd])
     AC_CHECK_FUNCS([gnutls_cipher_encrypt])
     CFLAGS="$OLD_CFLAGS"
     LIBS="$OLD_LIBS"

src/util/vircrypto.c

@@ -336,7 +336,7 @@ virCryptoGenerateRandom(size_t nbytes)
     if (VIR_ALLOC_N(buf, nbytes) < 0)
         return NULL;
 
-#if HAVE_GNUTLS_RND
+#if WITH_GNUTLS
     /* Generate the byte stream using gnutls_rnd() if possible */
     if ((ret = gnutls_rnd(GNUTLS_RND_RANDOM, buf, nbytes)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR,