docs/driver-model: Update device class docs

The driver model documentation was added to the kernel tree before
struct class was added to <linux/device.h>. Hence this patch that
updates the paragraph about struct class in
Documentation/driver-model/binding.txt.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/driver-model/binding.txt

@@ -48,10 +48,6 @@ devclass_add_device is called to enumerate the device within the class
 and actually register it with the class, which happens with the
 class's register_dev callback.
 
-NOTE: The device class structures and core routines to manipulate them
-are not in the mainline kernel, so the discussion is still a bit
-speculative. 
-
 
 Driver
 ~~~~~~