css: Remove old animation code

Deprecate public API where appropriate and make it no-ops.
Remove all calls to it.
Get rid of the 'transition' css property.

For now, this means spinners don't animate anymore.

gtk/gtkstyleproperties.c

@@ -26,7 +26,6 @@
 #include "gtkstyleprovider.h"
 #include "gtksymboliccolor.h"
 #include "gtkthemingengine.h"
-#include "gtkanimationdescription.h"
 #include "gtkgradient.h"
 #include "gtkcssshadowvalueprivate.h"
 #include "gtkcssshorthandpropertyprivate.h"