build: Remove the empty variable assignment

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

libs/libc/zoneinfo/Makefile

@@ -35,11 +35,6 @@
 
 include $(TOPDIR)/Make.defs
 
-# Zoneinfo database
-
-ASRCS =
-CSRCS =
-
 ifeq ($(CONFIG_LIB_ZONEINFO_ROMFS),y)
 CSRCS += tzromfs.c
 endif
@@ -54,12 +49,8 @@ ZONEINFO_PATH = $(TOPDIR)/libs/libc/zoneinfo
 TZBIN_PATH = $(ZONEINFO_PATH)/tzbin
 TZCODE_PATH = $(ZONEINFO_PATH)/tzcode
 
-ROOTDEPPATH = --dep-path .
-
 # Common build
 
-VPATH =
-
 all: .built
 .PHONY: romfs register context depend clean distclean
 
@@ -128,7 +119,7 @@ context: .tzbuilt romfs
 # Create dependencies
 
 .depend: Makefile $(SRCS)
-	$(Q) $(MKDEP) $(ROOTDEPPATH) "$(CC)" -- $(CFLAGS) -- $(SRCS) >Make.dep
+	$(Q) $(MKDEP) "$(CC)" -- $(CFLAGS) -- $(SRCS) >Make.dep
 	$(Q) touch $@
 
 depend: .depend