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>

include/iscsi-private.h

@@ -31,10 +31,6 @@
 extern "C" {
 #endif
 
-#ifndef discard_const
-#define discard_const(ptr) ((void *)((intptr_t)(ptr)))
-#endif
-
 #ifndef MIN
 #define MIN(a, b) (((a) < (b)) ? (a) : (b))
 #endif

include/iscsi.h

@@ -549,12 +549,12 @@ EXTERN int iscsi_logout_sync(struct iscsi_context *iscsi);
 
 struct iscsi_target_portal {
        struct iscsi_target_portal *next;
-       const char *portal;
+       char *portal;
 };
 
 struct iscsi_discovery_address {
        struct iscsi_discovery_address *next;
-       const char *target_name;
+       char *target_name;
        struct iscsi_target_portal *portals;
 };