s390: get rid of exit_thread()

exit_thread() is empty now. Therefore remove it and get rid of a
pointless branch.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -142,7 +142,6 @@ config S390
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
-	select HAVE_EXIT_THREAD
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER

arch/s390/kernel/process.c

@@ -43,13 +43,6 @@ asmlinkage void ret_from_fork(void) asm ("ret_from_fork");
 
 extern void kernel_thread_starter(void);
 
-/*
- * Free current thread data structures etc..
- */
-void exit_thread(struct task_struct *tsk)
-{
-}
-
 void flush_thread(void)
 {
 }