include/linux/poison.h: remove obsolete comment

When the definition was changed, the comment became stale.  Just remove
it since there isn't anything useful to say here.

Fixes: b8a0255d ("include/linux/poison.h: use POISON_POINTER_DELTA for poison pointers")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Vasily Kulikov <segoon@openwall.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20200730174108.GJ23808@casper.infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>