Remove 'gnutls_secure_malloc' (see
<https://gitorious.org/gnutls/gnutls/commit/f42e825d96b06f7069e4e9e8011a3ea8b93b4382>).

Patch by Ludovic Courtès <ludo@gnu.org>.

--- gnutls-3.3.1/guile/src/core.c-orig	2014-04-23 01:24:26.455377062 +0400
+++ gnutls-3.3.1/guile/src/core.c	2014-04-23 01:25:14.489068473 +0400
@@ -3366,7 +3366,6 @@
   /* Use Guile's allocation routines, which will run the GC if need be.  */
   gnutls_malloc = scm_malloc;
   gnutls_realloc = scm_realloc;
-  gnutls_secure_malloc = scm_malloc;
   gnutls_free = free;
 
   (void) gnutls_global_init ();