XML error handling code in `utils.js` is never reached

[simon-20]

Brief Description
In utils.js, there is code in the execXmllint function which raises an exception if xmllint returns an error code when parsing the XML. However, it appears that this code will never be reached, because xmllint is called with the --recover option, and this option means that xmllint always returns 0/success. This error handling code should be removed to avoid confusion for developers down the line.

There is also code in validatorServices.js to handle the exception raised by the xmllint error handling code above (the code which should raise an exception, but which in fact will never do so). This will never be reached when parsing errors are encountered, since the exception will never be thrown. It may, however, be reached if for whatever reason Node was unable to start xmllint, so this exception handling code may not be safe to remove.

Severity
Low

[simon-20]

I have left this code in there for now, and not removed it in PR #548, because the function name is general and needs proper investigation as to whether it is used elsewhere, outside above context.