Makefile.headersinst: remove destination-y option

This option was added in commit c7bb349e7c ("kbuild: introduce destination-y
for exported headers") but never used in-tree.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.headersinst

@@ -14,7 +14,7 @@ kbuild-file := $(srctree)/$(obj)/Kbuild
 include $(kbuild-file)
 
 # called may set destination dir (when installing to asm/)
-_dst := $(if $(destination-y),$(destination-y),$(if $(dst),$(dst),$(obj)))
+_dst := $(if $(dst),$(dst),$(obj))
 
 old-kbuild-file := $(srctree)/$(subst uapi/,,$(obj))/Kbuild
 ifneq ($(wildcard $(old-kbuild-file)),)