memorder: Remove redundant footnote

Now that it becomes contextually obvious that this paragraph is
talking on the pre-v4.15 READ_ONCE() of Alpha, the footnote can be
removed.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
1 file changed