s390/irq: remove HAVE_IRQ_EXIT_ON_IRQ_STACK

This is no longer true since we switched to generic entry. The code
switches to the IRQ stack before calling do_IRQ, but switches back
to the kernel stack before calling irq_exit().

Fixes: 56e62a73 ("s390: convert to generic entry")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/Kconfig

@@ -163,7 +163,6 @@ config S390
 	select HAVE_GCC_PLUGINS
 	select HAVE_GENERIC_VDSO
 	select HAVE_IOREMAP_PROT if PCI
-	select HAVE_IRQ_EXIT_ON_IRQ_STACK
 	select HAVE_KERNEL_BZIP2
 	select HAVE_KERNEL_GZIP
 	select HAVE_KERNEL_LZ4