kbuild: remove build_unifdef target in scripts/Makefile

Since commit 2aedcd09 ("kbuild: suppress annoying "... is up to date."
message"), if_changed and friends nicely suppress "is up to date" messages.

We do not need per-Makefile tricks.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -1182,7 +1182,7 @@ PHONY += archheaders archscripts
 
 PHONY += __headers
 __headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
-	$(Q)$(MAKE) $(build)=scripts build_unifdef
+	$(Q)$(MAKE) $(build)=scripts scripts/unifdef
 
 PHONY += headers_install
 headers_install: __headers

scripts/Makefile

@@ -31,11 +31,6 @@ always		:= $(hostprogs-y) $(hostprogs-m)
 # The following hostprogs-y programs are only build on demand
 hostprogs-y += unifdef
 
-# These targets are used internally to avoid "is up to date" messages
-PHONY += build_unifdef
-build_unifdef: $(obj)/unifdef
-	@:
-
 subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-$(CONFIG_SECURITY_SELINUX) += selinux