uapi/linux/target_core_user.h: fix headers_install.sh badness

scripts/headers_install.sh will transform __packed to
__attribute__((packed)), so the #ifndef is not necessary.
(and, in fact, it's problematic, because we'll end up with the header
 containing:
#ifndef __attribute__((packed))
#define __attribu...
and so forth.)

Cc: stable@vger.kernel.org # 3.18
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

include/uapi/linux/target_core_user.h

@@ -6,10 +6,6 @@
 #include <linux/types.h>
 #include <linux/uio.h>
 
-#ifndef __packed
-#define __packed                        __attribute__((packed))
-#endif
-
 #define TCMU_VERSION "1.0"
 
 /*