code cleanup: simplify speed.fast_settings.

speed.fast_settings[] was introduced in 7b2eecc724 to be used with
Sonic. Looks like after 7b2eecc724 the code related to everything
except fast_settings[0] was removed.

Might be that speed.fast_settings[0] is also irrelevant and could be
removed.

src/libespeak-ng/setlengths.c

 
 	if (control & 2)
 		DoSonicSpeed(1 * 1024);
-	if ((wpm_value >= espeakRATE_MAXIMUM) || ((wpm_value > speed.fast_settings[0]) && (wpm > 350))) {
+	if ((wpm_value >= espeakRATE_MAXIMUM) || ((wpm_value > speed.fast_settings) && (wpm > 350))) {
 		wpm2 = wpm;
 		wpm = espeakRATE_NORMAL;
 

src/libespeak-ng/synthesize.h

 	int lenmod_factor;
 	int lenmod2_factor;
 	int min_sample_len;
-	int fast_settings[8];
+	int fast_settings;	// TODO: rename this variable to better explain the purpose, or delete if there is none
 } SPEED_FACTORS;
 
 typedef struct {

src/libespeak-ng/voices.c

 	voice->samplerate = samplerate_native;
 	memset(voice->klattv, 0, sizeof(voice->klattv));
 
-	speed.fast_settings[0] = espeakRATE_MAXIMUM;
-	speed.fast_settings[1] = 800;
-	speed.fast_settings[2] = espeakRATE_NORMAL;
+	speed.fast_settings = espeakRATE_MAXIMUM;
 
 	voice->roughness = 2;
 
 			voice->klattv[KLATT_Kopen] -= 40;
 			break;
 		case V_FAST:
-			Read8Numbers(p, speed.fast_settings);
+			sscanf(p, "%d", &speed.fast_settings);
 			SetSpeed(3);
 			break;
 		case V_DICTMIN: