xdiff: remove duplicate headers from xhistogram.c

8c912ee ("teach --histogram to diff", 2011-07-12) included them, but
were already part of xinclude.h

Signed-off-by: Carlo Marcelo Arenas Belón <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: carenas

xdiff/xhistogram.c

@@ -42,8 +42,6 @@
  */
 
 #include "xinclude.h"
-#include "xtypes.h"
-#include "xdiff.h"
 
 #define MAX_PTR	UINT_MAX
 #define MAX_CNT	UINT_MAX