busybox: don't install NTP scripts if NTP isn't configured

If you're using Chrony or NTPD you don't want the busybox NTP server
as well.  Make it's installation truly conditional.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name> [simplify]

package/utils/busybox/Makefile

@@ -112,9 +112,13 @@ endef
 define Package/busybox/install
 	$(INSTALL_DIR) $(1)/etc/init.d
 	$(CP) $(PKG_INSTALL_DIR)/* $(1)/
+ifneq ($(CONFIG_BUSYBOX_CONFIG_CROND),)
 	$(INSTALL_BIN) ./files/cron $(1)/etc/init.d/cron
+endif
+ifneq ($(CONFIG_BUSYBOX_CONFIG_NTPD),)
 	$(INSTALL_BIN) ./files/sysntpd $(1)/etc/init.d/sysntpd
 	$(INSTALL_BIN) ./files/ntpd-hotplug $(1)/usr/sbin/ntpd-hotplug
+endif
 	-rm -rf $(1)/lib64
 endef