block: remove refs to XD disks from documentation

Commit d1a6f4f19728d6e90480e53601a90fc9f6a348ad
"block: delete super ancient PC-XT driver for 1980's hardware"
deleted the XD disk driver, but there are still a few
references to it in the documentation directory. Delete
the remnants and thus also free up the major block device
13 for reuse.

Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/Documentation/devices.txt b/Documentation/devices.txt
index 08f01e7..b901591 100644
--- a/Documentation/devices.txt
+++ b/Documentation/devices.txt
@@ -498,12 +498,8 @@
 
 		Each device type has 5 bits (32 minors).
 
- 13 block	8-bit MFM/RLL/IDE controller
-		  0 = /dev/xda		First XT disk whole disk
-		 64 = /dev/xdb		Second XT disk whole disk
-
-		Partitions are handled in the same way as IDE disks
-		(see major number 3).
+ 13 block	Previously used for the XT disk (/dev/xdN)
+		Deleted in kernel v3.9.
 
  14 char	Open Sound System (OSS)
 		  0 = /dev/mixer	Mixer control