SynthStatus is not called, so remove it.

src/libespeak-ng/synthesize.c

 	return 0;
 }
 
-int SynthStatus()
-{
-	return timer_on;
-}
-
 int SpeakNextClause(FILE *f_in, const void *text_in, int control)
 {
 	// Speak text from file (f_in) or memory (text_in)

src/libespeak-ng/synthesize.h

 void MakeWave2(PHONEME_LIST *p, int n_ph);
 int  SynthOnTimer(void);
 int  SpeakNextClause(FILE *f_text, const void *text_in, int control);
-int  SynthStatus(void);
 void SetSpeed(int control);
 void SetEmbedded(int control, int value);
 void SelectPhonemeTable(int number);