WVoiceChanged is not used, so remove it.

src/libespeak-ng/speech.c

 char path_home[N_PATH_HOME]; // this is the espeak-data directory
 extern int saved_parameters[N_SPEECH_PARAM]; // Parameters saved on synthesis start
 
-void WVoiceChanged(voice_t *wvoice)
-{
-	// Voice change in wavegen
-	voice_samplerate = wvoice->samplerate;
-}
-
 static int dispatch_audio(short *outbuf, int length, espeak_EVENT *event)
 {
 	int a_wave_can_be_played = 1;

src/libespeak-ng/voice.h

 voice_t *LoadVoice(const char *voice_name, int control);
 voice_t *LoadVoiceVariant(const char *voice_name, int variant);
 espeak_ng_STATUS DoVoiceChange(voice_t *v);
-void WVoiceChanged(voice_t *wvoice);
 void WavegenSetVoice(voice_t *v);
 void ReadTonePoints(char *string, int *tone_pts);
 void VoiceReset(int control);