c6x: remove unused KTHREAD_SIZE definition

KTHREAD_SIZE has never been used since it has been defined for c6x arch.
Let's remove this useless definition.
Signed-off-by: Jérémy Lefaure <jeremy.lefaure@lse.epita.fr>
Signed-off-by: Mark Salter <msalter@redhat.com>

arch/c6x/kernel/asm-offsets.c

@@ -107,7 +107,6 @@ void foo(void)
 	/* These would be unneccessary if we ran asm files
 	 * through the preprocessor.
 	 */
-	DEFINE(KTHREAD_SIZE, THREAD_SIZE);
 	DEFINE(KTHREAD_SHIFT, THREAD_SHIFT);
 	DEFINE(KTHREAD_START_SP, THREAD_START_SP);
 	DEFINE(ENOSYS_, ENOSYS);