logical-monitor: Don't mirror physical dimensions

Don't try to mirror the physical dimension, since that's a property of
one of the monitors, not of the logical monitor. Callers are changed to
deal with choosing the monitor to represent the logical monitor.

https://bugzilla.gnome.org/show_bug.cgi?id=777732

src/wayland/meta-wayland-outputs.c

@@ -99,8 +99,8 @@ send_output_events (struct wl_resource *resource,
       wl_output_send_geometry (resource,
                                logical_monitor->rect.x,
                                logical_monitor->rect.y,
-                               logical_monitor->width_mm,
-                               logical_monitor->height_mm,
+                               output->width_mm,
+                               output->height_mm,
                                output->subpixel_order,
                                output->vendor,
                                output->product,