Library internal only C preprocessor macros FORMAT_OFF_T and FORMAT_OFF_TU

remain in use as internal curl_off_t print formatting strings for the internal
*printf functions which still cannot handle print formatting string directives
such as "I64d", "I64u", and others available on MSVC, MinGW, Intel's ICC, and
other DOS/Windows compilers.

This reverts previous commit part which did:

FORMAT_OFF_T  -> CURL_FORMAT_CURL_OFF_T
FORMAT_OFF_TU -> CURL_FORMAT_CURL_OFF_TU

lib/formdata.c

@@ -1674,7 +1674,7 @@ int main(int argc, argv_item_t argv[])
   } while(1);
 
   fprintf(stdout, "size: ");
-  fprintf(stdout, "%" CURL_FORMAT_CURL_OFF_T, size);
+  fprintf(stdout, "%" FORMAT_OFF_T, size);
   fprintf(stdout, "\n");
   if(errors)
     fprintf(stdout, "\n==> %d Test(s) failed!\n", errors);