config.mk: delete unnecessary lines

SPL_BIN is already defined in spl/Makefile
and it is used only in spl/Makefile.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/config.mk b/config.mk
index 3441387..206de20 100644
--- a/config.mk
+++ b/config.mk
@@ -13,12 +13,6 @@
 
 export	SHELL
 
-ifeq ($(CONFIG_TPL_BUILD),y)
-SPL_BIN := u-boot-tpl
-else
-SPL_BIN := u-boot-spl
-endif
-
 ifeq ($(CURDIR),$(SRCTREE))
 dir :=
 else