Remove calls to miInitializeBackingStore() and includes of mibstore.h

mibstore.h defines miInitializeBackingStore() as an empty stub, and
goes away in xserver 1.14.

driver/xf86-video-sunffb/src/ffb_driver.c

@@ -30,7 +30,6 @@
 #include "xf86.h"
 #include "xf86_OSproc.h"
 #include "mipointer.h"
-#include "mibstore.h"
 #include "micmap.h"
 #include "fb.h"
 
@@ -761,8 +760,6 @@ FFBScreenInit(int scrnIndex, ScreenPtr pScreen, int argc, char **argv)
 	xf86Msg(X_INFO, "%s: Using acceleration\n", pFfb->psdp->device);
     }
 
-
-    miInitializeBackingStore(pScreen);
     xf86SetBackingStore(pScreen);
     xf86SetSilkenMouse(pScreen);