virgl: remove sw_winsys pointer from virgl_screen

The screen already has a pointer to the (base) winsys object.
With the latter of which implemented/sub-classed as either drm or sw
based one, depending on the target.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/gallium/drivers/virgl/virgl_public.h

@@ -24,7 +24,6 @@
 #define VIRGL_PUBLIC_H
 
 struct pipe_screen;
-struct sw_winsys;
 struct virgl_winsys;
 
 struct pipe_screen *

src/gallium/drivers/virgl/virgl_screen.c

@@ -532,7 +532,6 @@ virgl_create_screen(struct virgl_winsys *vws)
       return NULL;
 
    screen->vws = vws;
-   screen->winsys = NULL;
    screen->base.get_name = virgl_get_name;
    screen->base.get_vendor = virgl_get_vendor;
    screen->base.get_param = virgl_get_param;

src/gallium/drivers/virgl/virgl_screen.h

@@ -31,7 +31,6 @@
 #include "pipe/p_screen.h"
 struct virgl_screen {
    struct pipe_screen base;
-   struct sw_winsys *winsys;
    struct virgl_winsys *vws;
 
    struct virgl_drm_caps caps;