kbuild: remove unused RANLIB

RANLIB was added by commit e221174 (more than a decade ago)
but it has been never referenced at all.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/Makefile b/Makefile
index 1df3f70..2fa0966 100644
--- a/Makefile
+++ b/Makefile
@@ -354,7 +354,6 @@
 OBJCOPY		= $(CROSS_COMPILE)objcopy
 OBJDUMP		= $(CROSS_COMPILE)objdump
 AWK		= awk
-RANLIB		= $(CROSS_COMPILE)RANLIB
 DTC		= dtc
 CHECK		= sparse