use style autoloading

avoids a deprecation warning; the function is not even deprecated, the vala
bindings just have a bug here, but this also fixes it

src/audrey.gresource.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gresources>
   <gresource prefix="/eu/callcc/audrey">
-    <file>audrey.css</file>
+    <file>style.css</file>
     <file preprocess="xml-stripblanks">gtk/help-overlay.ui</file>
     <file preprocess="xml-stripblanks">ui/play_queue.ui</file>
     <file preprocess="xml-stripblanks">ui/setup.ui</file>

src/ui/window.vala

@@ -31,11 +31,6 @@ class Ui.Window : Adw.ApplicationWindow {
 
     public Window (Gtk.Application app) {
         Object (application: app);
-
-        var provider = new Gtk.CssProvider ();
-        provider.load_from_resource("/eu/callcc/audrey/audrey.css");
-
-        Gtk.StyleContext.add_provider_for_display (Gdk.Display.get_default (), provider, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION);
     }
 
     construct {