Documentation: remove reference to pktcdvd in cdrom documentation

pktcdvd got killed in a previous commit, remove the reference to it as
well in the cdrom documentation.

Fixes: 1cea518 ("block: remove pktcdvd driver")
Reported-by: Stephen Rothwell <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: axboe

Documentation/cdrom/index.rst

@@ -8,7 +8,6 @@ CD-ROM
     :maxdepth: 1
 
     cdrom-standard
-    packet-writing
 
 .. only::  subproject and html