Stop passing around MetaFrameBorders

Instead of passing around MetaFrameBorders, compute it when we need it.
This also allows us to know that we are using MetaFrameBorders only for windows
with frames (where it is meaningful) and not for frameless windows, which
can have custom borders which we need to interpret differently.

https://bugzilla.gnome.org/show_bug.cgi?id=707194

src/core/constraints.h

@@ -40,7 +40,6 @@ typedef enum
 } MetaMoveResizeFlags;
 
 void meta_window_constrain (MetaWindow          *window,
-                            MetaFrameBorders    *orig_borders,
                             MetaMoveResizeFlags  flags,
                             int                  resize_gravity,
                             const MetaRectangle *orig,