Remove confusing sc_str_truncate()

This util function was error-prone:
 - it accepted a buffer as parameter (not necessarily a NUL-terminated
   string) and its length (including the NUL char, if any);
 - it wrote '\0' over the last character of the buffer, so the last
   character was lost if the buffer was not a NUL-terminated string, and
   even worse, it caused undefined behavior if the length was empty;
 - it returned the length of the resulting NUL-terminated string,
   which was inconsistent with the input buffer length.

In addition, it was not necessarily optimal:
 - it wrote '\0' twice;
 - it required to know the buffer length, that is the input string
   length + 1, in advance.

Remove this function, and let the client use strcspn() manually.

app/src/util/str.c

@@ -297,14 +297,6 @@ error:
     return NULL;
 }
 
-size_t
-sc_str_truncate(char *data, size_t len, const char *endchars) {
-    data[len - 1] = '\0';
-    size_t idx = strcspn(data, endchars);
-    data[idx] = '\0';
-    return idx;
-}
-
 ssize_t
 sc_str_index_of_column(const char *s, unsigned col, const char *seps) {
     size_t colidx = 0;