depend instead of select on zlib/png to shut up Kconfig warning

(doesn't change anything as xorg already depends on them)

package/dillo/Config.in

@@ -1,12 +1,12 @@
 config BR2_PACKAGE_DILLO
 	bool "dillo"
 	default n
-	select BR2_PACKAGE_ZLIB
 	select BR2_PACKAGE_JPEG
-	select BR2_PACKAGE_LIBPNG
 	select BR2_PACKAGE_LIBGLIB12
 	select BR2_PACKAGE_LIBGTK12
 	depends BR2_PACKAGE_XORG
+	depends BR2_PACKAGE_ZLIB
+	depends BR2_PACKAGE_LIBPNG
 	help
 	  Dillo is a small GTK+ based web browser written in C.