Removing the unused features

dnn/dump_data.c

dnn/include/lpcnet.h

dnn/lpcnet.c

dnn/lpcnet_dec.c

dnn/lpcnet_demo.c

dnn/lpcnet_enc.c

dnn/test_lpcnet.c

dnn/training_tf2/lpcnet.py

dnn/training_tf2/test_lpcnet.py

dnn/training_tf2/train_lpcnet.py