apparmor: Remove unnecessary NULL check before kvfree()

Since kvfree() already checks if its argument is NULL, an additional
check before calling kvfree() is unnecessary and can be removed.

Remove it and the following Coccinelle/coccicheck warning reported by
ifnullfree.cocci:

  WARNING: NULL check before some freeing functions is not needed

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: John Johansen <john.johansen@canonical.com>