Removes references to mibstore.h and miInitializeBackingStore, which
have been removed from xorg-server.  Zack Rusin <zackr@vmware.com>
wrote: "It was a noop for at least 5 years and it has been removed."
See: http://patches.openembedded.org/patch/46133/

--- xf86-video-trident-1.3.6/src/trident_driver.c.~1~	2012-07-15 22:16:00.000000000 -0400
+++ xf86-video-trident-1.3.6/src/trident_driver.c	2014-12-19 01:45:29.529410518 -0500
@@ -56,7 +56,6 @@
 
 #include "mipointer.h"
 
-#include "mibstore.h"
 #include "shadow.h"
 #include "trident.h"
 #include "trident_regs.h"
@@ -3037,7 +3036,6 @@
     	TridentAccelInit(pScreen);
     }
 
-    miInitializeBackingStore(pScreen);
     xf86SetBackingStore(pScreen);
 
     /* Initialise cursor functions */