vga_int: remove unused function protype

Signed-off-by: Nyuchenlin <yuchenlin@synology.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20181022080053.9379-1-yuchenlin@synology.com>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

hw/display/vga_int.h

@@ -166,7 +166,6 @@ MemoryRegion *vga_init_io(VGACommonState *s, Object *obj,
                           const MemoryRegionPortio **vbe_ports);
 void vga_common_reset(VGACommonState *s);
 
-void vga_sync_dirty_bitmap(VGACommonState *s);
 void vga_dirty_log_start(VGACommonState *s);
 void vga_dirty_log_stop(VGACommonState *s);