release-small: Don't attempt to access "dbus.libs", etc., don't exist

dbus_libs and others do, but they're deprecated.

Just build 'dbus', these are now its various outputs.

pkgs/top-level/release-small.nix

···
   cpio = all;
   cron = linux;
   cups = linux;
+  dbus = linux;
   dhcp = linux;
   diffutils = all;
   e2fsprogs = linux;
···
   xkeyboard_config = linux;
   zile = linux;
   zip = all;
-
-  dbus = {
-    libs = linux;
-    daemon = linux;
-    tools = linux;
-  };
 
 } ))