lavfi/af_anequalizer: remove cabs, cexp dependencies

Replaces by real arithmetic. Tested the validity of these transformations separately.
Numerical differences are ~1e-15, and should not matter: it is not even
clear which is more precise mathematically.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
