hdpi: Revert hacks

Revert the hacks that where added in response to a bug caused by
commit ba459f4d202

https://bugzilla.gnome.org/show_bug.cgi?id=705410
shell_global: Use correct agruments for in update_scale_factor

Otherwise we crash ...

https://bugzilla.gnome.org/show_bug.cgi?id=705410