Line breaks in REDCap to LINST for HTML fields

In the `redcap2linst.php` script, it seems that on some REDCap versions, line breaks present in the REDCap fields that contain HTML are also added to the generated LINST (not only through `<br />` but also through real line breaks). This is a problem because LINST should only have one line per field, and thus line breaks present in the HTML should be removed.