cleanup: remove duplicate StringToWord()

Found with pmd-cpd static analysis

src/libespeak-ng/common.c

 	return acc;
 }
 
+unsigned int StringToWord(const char *string)
+{
+	// Pack 4 characters into a word
+	int ix;
+	unsigned char c;
+	unsigned int word;
+
+	if (string == NULL)
+		return 0;
+
+	word = 0;
+	for (ix = 0; ix < 4; ix++) {
+		if (string[ix] == 0) break;
+		c = string[ix];
+		word |= (c << (ix*8));
+	}
+	return word;
+}
+
 int towlower2(unsigned int c, Translator *translator)
 {
 	// check for non-standard upper to lower case conversions

src/libespeak-ng/common.h

 int isspace2(unsigned int c);
 int is_str_totally_null(const char* str, int size); // Tests if all bytes of str up to size are null
 int Read4Bytes(FILE *f);
+unsigned int StringToWord(const char *string);
 int towlower2(unsigned int c, Translator *translator); // Supports Turkish I
 
 ESPEAK_NG_API int utf8_in(int *c, const char *buf);

src/libespeak-ng/compiledata.c

 #include <espeak-ng/speak_lib.h>
 #include <espeak-ng/encoding.h>
 
-#include "common.h"                    // for GetFileLength, strncpy0, ...
+#include "common.h"                    // for GetFileLength, strncpy0, ...c
 #include "error.h"                    // for create_file_error_context
 #include "mnemonics.h"               // for LookupMnemName, MNEM_TAB
 #include "phoneme.h"                  // for PHONEME_TAB, PHONEME_TAB_LIST
 		error("%s.", message);
 }
 
-static unsigned int StringToWord(const char *string)
-{
-	// Pack 4 characters into a word
-	int ix;
-	unsigned char c;
-	unsigned int word;
-
-	if (string == NULL)
-		return 0;
-
-	word = 0;
-	for (ix = 0; ix < 4; ix++) {
-		if (string[ix] == 0) break;
-		c = string[ix];
-		word |= (c << (ix*8));
-	}
-	return word;
-}
-
 static const MNEM_TAB reserved_phonemes[] = {
 	{ "_\001",  phonCONTROL },      // NOT USED
 	{ "%",      phonSTRESS_U },

src/libespeak-ng/compilembrola.c

 #include "mbrola.h"
 
 #include "error.h"                // for create_file_error_context
+#include "common.h"               // for StringToWord
 #include "mbrola.h"               // for MBROLA_TAB
 #include "phoneme.h"              // for N_PHONEME_TAB
 #include "speech.h"               // for path_home
 	return current == filename ? current : current + 1;
 }
 
-static unsigned int StringToWord(const char *string)
-{
-	// Pack 4 characters into a word
-	int ix;
-	unsigned char c;
-	unsigned int word;
-
-	if (string == NULL)
-		return 0;
-
-	word = 0;
-	for (ix = 0; ix < 4; ix++) {
-		if (string[ix] == 0) break;
-		c = string[ix];
-		word |= (c << (ix*8));
-	}
-	return word;
-}
-
 #pragma GCC visibility push(default)
 espeak_ng_STATUS espeak_ng_CompileMbrolaVoice(const char *filepath, FILE *log, espeak_ng_ERROR_CONTEXT *context)
 {