Adwaita.css: Remove custom development styling

GTK now includes it's own styling for development versions,
so Nautilus doesn't need to include it's own.
3 jobs for master in 8 minutes and 54 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #185162
flatpak devel

00:08:02

9.1%
 
  Deploy
passed #185163
pages

00:00:51

passed pages:deploy

00:00:00