[TASK] Remove the theme style checking hack

Submitted by Andre Miranda @andreldm

Assigned to Eric Koegel

Link to original bug (#15228)

Description

This is a follow-up of Bug #13928, the current way to check if a theme declares some style or not in order to apply a default one is very inefficient (all the theme has to serialized into a string). As I see, the options are:

• Use a white list to skip that check for some themes (e.g. Greybird)
• Ask upstream to why the GTK_STYLE_PROVIDER_PRIORITY_* doesn't work for this use case (more details on Bug #13928 and https://gitlab.gnome.org/GNOME/glib/issues/1698)

Version: 4.13.3