code cleanup: remove unused #defines

Note: Strange that FLAG_ALT7 is used but ALT4-ALT6 are not. Same with
R6p.

src/libespeak-ng/klatt.h

 #define Rnpp 10
 #define R1p  11
 #define R2p  12
-#define R3p  13
-#define R4p  14
-#define R5p  15
 #define R6p  16
 
 #define RGL  17

src/libespeak-ng/spect.h

 
 #define FRAME_WIDTH  1000  // max width for 8000kHz frame
 #define MAX_DISPLAY_FREQ 9500
-#define FRAME_HEIGHT 240
 
 #define T_AMPLITUDE 308
 #define T_AV      312

src/libespeak-ng/translate.h

 #define FLAG_ALT_TRANS      0x8000 // language specific
 #define FLAG_ALT2_TRANS    0x10000 // language specific
 #define FLAG_ALT3_TRANS    0x20000 // language specific
-#define FLAG_ALT4_TRANS    0x40000 // language specific
-#define FLAG_ALT5_TRANS    0x80000 // language specific
-#define FLAG_ALT6_TRANS   0x100000 // language specific
 #define FLAG_ALT7_TRANS   0x200000 // language specific
 
 #define FLAG_COMBINE      0x800000 // combine with the next word