kconfig: remove always false ifeq ($(KBUILD_DEFCONFIG,) conditional

With the following two commits applied, all the arch Makefiles
define KBUILD_DEFCONFIG.

- Commit f3e20ad6 ("s390: move arch/s390/defconfig to
  arch/s390/configs/defconfig")

- Commit 986a1376 ("alpha: move arch/alpha/defconfig to
  arch/alpha/configs/defconfig")

The first conditional in the defconfig rule is always false.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/Makefile

@@ -74,9 +74,7 @@ savedefconfig: $(obj)/conf
 	$< $(silent) --$@=defconfig $(Kconfig)
 
 defconfig: $(obj)/conf
-ifeq ($(KBUILD_DEFCONFIG),)
-	$< $(silent) --defconfig $(Kconfig)
-else ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)),)
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)),)
 	@$(kecho) "*** Default configuration is based on '$(KBUILD_DEFCONFIG)'"
 	$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG) $(Kconfig)
 else