Btrfs: remove duplicated #include

Removed duplicated #include "compat.h"in
fs/btrfs/extent-tree.c

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/extent-tree.c

@@ -29,7 +29,6 @@
 #include "volumes.h"
 #include "locking.h"
 #include "ref-cache.h"
-#include "compat.h"
 
 #define PENDING_EXTENT_INSERT 0
 #define PENDING_EXTENT_DELETE 1