Remove the discard_const() macro

Declare dynamically allocated strings as 'char *' instead of 'const char *'.
Remove the discard_const() macro. Do not test whether or not a pointer is
NULL before calling free() because it is allowed to pass NULL to free().

Signed-off-by: Bart Van Assche <bvanassche@acm.org>

lib/sync.c

@@ -1828,11 +1828,12 @@ void iscsi_free_discovery_data(struct iscsi_context *iscsi _U_,
 
                 while (da->portals) {
                         struct iscsi_target_portal *ponext = da->portals->next;
-                        free(discard_const(da->portals->portal));
+
+                        free(da->portals->portal);
                         free(da->portals);
                         da->portals = ponext;
                 }
-                free(discard_const(da->target_name));
+                free(da->target_name);
                 free(da);
                 da = danext;
         }