Don't manipulate size/pos of fullscreen containers

In fullscreen mode position/dimensions of the fullscreen container were
being changed and then restored on unfullscreen. This would break things
that manipulated those dimensions while the window was fullscreen.
Instead have the rendering code handle the positioning directly and
leave the container information alone.

Fixes #3547

include/sway/tree/container.h

@@ -85,8 +85,6 @@ struct sway_container {
 	// Includes borders
 	double x, y;
 	double width, height;
-	double saved_x, saved_y;
-	double saved_width, saved_height;
 
 	// These are in layout coordinates.
 	double content_x, content_y;