staging: android: ion: Remove leftover comment

Since we use CMA APIs directly there is no device nor private heaps data,
drop this comment.

Fixes: 204f6722 ("staging: android: ion: Use CMA APIs directly")
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>