The ad-hoc pi constant has a ludicrous number of digits that offer no
value whatsoever. M_PI is more consistent and readable across the
codebase.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>