Remove unused functions (modelica#4061)

Note that they were previously used by get_token which was removed in modelica#3783

Modelica/Resources/C-Sources/ModelicaStrings.c

@@ -186,21 +186,6 @@ int ModelicaStrings_skipWhiteSpace(_In_z_ const char* string, int i) {
 
 /* ----------------- utility functions used in scanXXX functions ----------- */
 
-static int InSet(const char* string, int i, const char* separators) {
-    /* Return true if string[i] is one of the characters in separators. */
-    return strchr(separators, string[i-1]) != NULL;
-}
-
-static int SkipNonWhiteSpaceSeparator(const char* string, int i, const char* separators) {
-    /* Return index in string of first character which is ws or character in separators,
-       or position of terminating nul.
-     */
-    while (string[i-1] != '\0' && (isspace((unsigned char)string[i-1]) || InSet(string, i, separators))) {
-        ++i;
-    }
-    return i;
-}
-
 static int MatchUnsignedInteger(const char* string, int start) {
     /* Starts matching character which make an unsigned integer. The matching
        begins at the start index (first char has index 1). Returns the number