s390: drop meaningless 'targets' from tools Makefile

'targets' should be specified to include .*.cmd files to evaluate
if_changed or friends.

Here, facility-defs.h and dis-defs.h are generated by filechk.

Because filechk does not generate .*.cmd file, the 'targets' addition
is meaningless. The filechk correctly updates the target when its
content is changed.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/tools/Makefile

@@ -6,7 +6,6 @@
 kapi := arch/$(ARCH)/include/generated/asm
 kapi-hdrs-y := $(kapi)/facility-defs.h $(kapi)/dis-defs.h
 
-targets += $(addprefix ../../../,$(kapi-hdrs-y))
 PHONY += kapi
 
 kapi:	$(kapi-hdrs-y)