dyndbg: drop obsolete comment on ddebug_proc_open

dyndbg: drop obsolete comment on ddebug_proc_open

commit 4bad78c55002 ("lib/dynamic_debug.c: use seq_open_private() instead of seq_open()")'

The commit was one of a tree-wide set which replaced open-coded
boilerplate with a single tail-call.  It therefore obsoleted the
comment about that boilerplate, clean that up now.

Acked-by: <jbaron@akamai.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200719231058.1586423-4-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>