BF 4.3.1 + Smith + Kalman

• Betaflight 4.3.1 plus SmithPredictor plus KalmanFilter.
• Since KalmanFilter code is such a huge memory hog, this test-build removes MavLink, PPM, and Servos.

smith predictor defaults (CLI only):

smith_predict_str = 50
Allowed range: 0 - 100

smith_predict_delay = 40
Allowed range: 0 - 60

smith_predict_filt_hz = 5
Allowed range: 1 - 10000

kalman defaults (CLI only):

imuf_q = 10000
Allowed range: 1000 - 16000

imuf_w = 32
Allowed range: 0 - 64