remove note to convert to sin_cos_tau instead sin_cos_pi

remove note to convert to sin_cos_tau instead sin_cos_pi

In the process of converting the code, I discovered that
it would not remove any operations from sin_cos and that sin_cos_pi
would require an additional multiplication to implement, since what
the software implementation would really need instead of sin_cos_tau
would be for the input to be expressed as a integer number of right-
angles (how many multiples of 90 degrees is the input angle).