Removed dependency on ndarray_stats. Not working lib.

src/rt/ppm.rs

@@ -5,7 +5,6 @@ use crate::{config::*, FreqWeighting, StandardFilterDescriptor};
 use crate::{daq::StreamMgr, Dcol};
 use crossbeam::channel::{unbounded, Receiver, Sender};
 use crossbeam::utils::Backoff;
-use ndarray_stats::QuantileExt;
 use parking_lot::Mutex;
 use std::default;
 use std::ops::DerefMut;