Replacing RNN_ macros with existing OPUS_ ones

dnn/common.h

dnn/dred_rdovae_dec.c

dnn/dred_rdovae_enc.c

dnn/dump_data.c

dnn/freq.c

dnn/lpcnet.c

dnn/lpcnet_demo.c

dnn/lpcnet_enc.c

dnn/lpcnet_plc.c

dnn/nnet.c

dnn/write_lpcnet_weights.c

silk/dred_encoder.c