view: use saved geometry for borders if needed

This fixes the issues caused by 60f06a1 and greatly simplifies the code.
Turns out we were already tracking the dimensions needed.

river/View.zig

@@ -262,16 +262,6 @@ pub fn getDefaultFloatBox(self: Self) Box {
     };
 }
 
-/// Return the dimensions of the actual "visible bounds" that the client has
-/// committed. This excludes any "invisible" areas of the surface that show
-/// useless stuff like CSD shadows.
-pub fn getActualBox(self: Self) Box {
-    return switch (self.impl) {
-        .xdg_toplevel => |xdg_toplevel| xdg_toplevel.getActualBox(),
-        .xwayland_view => |xwayland_view| xwayland_view.getActualBox(),
-    };
-}
-
 /// Called by the impl when the surface is ready to be displayed
 pub fn map(self: *Self) void {
     const root = self.output.root;