maintainability: remove some unused variables and unnecessary extern declarations

src/libespeak-ng/compiledict.c

 #include "translate.h"
 
 static FILE *f_log = NULL;
-extern char *dir_dictionary;
 
 extern char word_phonemes[N_WORD_PHONEMES];    // a word translated into phoneme codes
 

src/libespeak-ng/phoneme.h

 #define phonPAUSE_CLAUSE 27
 #define phonVOWELTYPES   28  // 28 to 33
 
-extern const unsigned char pause_phonemes[8];  // 0, vshort, short, pause, long, glottalstop
-
 #define N_PHONEME_TABS     150     // number of phoneme tables
 #define N_PHONEME_TAB      256     // max phonemes in a phoneme table
 #define N_PHONEME_TAB_NAME  32     // must be multiple of 4

src/libespeak-ng/spect.c

 #include "spect.h"
 #include "ieee80.h"
 
-extern unsigned char pk_shape1[];
-extern int pk_select;
 extern char voice_name[];
 
 static int frame_width;
-int pk_select;
 
 static int default_freq[N_PEAKS] =
 { 200, 500, 1200, 3000, 3500, 4000, 6900, 7800, 9000 };
 	spect->frames = NULL;
 	spect->name = NULL;
 
-	pk_select = 1;
 	spect->grid = 1;
 	spect->duration = 0;
 	spect->pitch1 = 0;

src/libespeak-ng/synthdata.c

 
 int wavefile_ix; // a wavefile to play along with the synthesis
 int wavefile_amp;
-int wavefile_ix2;
-int wavefile_amp2;
 
 int seq_len_adjust;
 int vowel_transition[4];
-int vowel_transition0;
-int vowel_transition1;
 
 static espeak_ng_STATUS ReadPhFile(void **ptr, const char *fname, int *size, espeak_ng_ERROR_CONTEXT *context)
 {

src/libespeak-ng/synthesize.h

 
 extern int wavefile_ix;
 extern int wavefile_amp;
-extern int wavefile_ix2;
-extern int wavefile_amp2;
 extern int vowel_transition[4];
-extern int vowel_transition0, vowel_transition1;
 
 #define N_ECHO_BUF 5500   // max of 250mS at 22050 Hz
 extern int echo_head;
 extern int formant_rate[];         // max rate of change of each formant
 extern SPEED_FACTORS speed;
 
-extern long count_samples;
 extern unsigned char *out_ptr;
 extern unsigned char *out_start;
 extern unsigned char *out_end;
-extern int event_list_ix;
 extern espeak_EVENT *event_list;
 extern t_espeak_callback *synth_callback;
 extern const char *version_string;
 extern const int version_phdata;
-extern double sonicSpeed;
 
 #define N_SOUNDICON_TAB  80   // total entries in soundicon_tab
 #define N_SOUNDICON_SLOTS 4    // number of slots reserved for dynamic loading of audio files

src/libespeak-ng/translate.c

 	return count;
 }
 
-extern char *phondata_ptr;
-
 static int TranslateWord3(Translator *tr, char *word_start, WORD_TAB *wtab, char *word_out)
 {
 	// word1 is terminated by space (0x20) character

src/libespeak-ng/translate.h

 	int flags;
 } ALPHABET;
 
-extern ALPHABET alphabets[];
 extern ALPHABET *current_alphabet;
 // alphabet flags
 #define AL_DONT_NAME    0x01 // don't speak the alphabet name
 extern int option_wordgap;
 
 extern int count_characters;
-extern int count_words;
 extern int count_sentences;
 extern int skip_characters;
 extern int skip_words;

src/libespeak-ng/wavegen.c

 
 int current_source_index = 0;
 
-extern FILE *f_wave;
-
 #if HAVE_SONIC_H
 static sonicStream sonicSpeedupStream = NULL;
 double sonicSpeed = 1.0;